A Glossary of Terms Related to Fasteners
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
A
Acorn Nut: Acorn Nut is one of the most common types of fasteners that can be found on the Market. It is an especially designed nut that is mostly used to protect against external threads. In some applications, it is necessary that the fastener not be in contact with any threads that connect it to the secondary bodies. In situations like these acorn nuts are used. They have the shape of the acorn on top and thus this is where it has its name originated from. In essence, it is a hexagonal nut type of a fastener.
Anti-Friction Coating: Anti-Friction Coating is the special type of a coating that is put up on the fastener, so that it will help protect against friction and it will also provide constant lubrication to the fastener. These types of applied materials are made from either molybdenum disulphide or graphite for maximum friction resistance. These materials prevent the contact between two metals, thus increasing the efficiency of the fastener and the material that it is bonded to. These types of coatings can be applied to all kinds of fasteners and they are especially used in Aerospace components for maximum safety.
Anti-Seize Compound: Anti-Seize Compound is a special type of a compound that is used in conjunction with fasteners in various applications. Anti-Seize compound will protect the fastener from corrosion as it will build a second barrier of resistance on the fastener. Most importantly, this compound can provide advanced water resistance so that moisture can not get in to between the two threads that the fastener is holding on to. If this compound is used with stainless steel fasteners, then its main purpose is to prevent galling between the two surfaces of the fastener threads. This is possibly the most common use of the compound.
Aerotight Nut: Aerotight Nut is a special type of a fastener that it especially constructed from metals for the sole purpose of torque pressure. There are two slotted parts that are apart from each other and when this special nut is fastened; the two slotted parts will cause extreme stiffness on their parts and these parts will exert pressure on the two external threads that the fastener is holding on to. It is mostly a way to create torque so that the fastener is holding on to the threads almost in an airtight position hence the name Aerotight Nut.
Age Hardening: This is a procedure that is applied on most fasteners and especially on bolts. It is used in the automotive sector as well as the aerospace sector for most bolts to create increased tensile strength. In this process, aging is done synthetically on the fastener. This is usually accomplished with the instant and rapid cooling of the fastener, once it is constructed. This way real life aging is stimulated and thus the strength of the fastener is increased. Also as an added effect the ductility (the ability to flex and flow of metals) of the fastener is also decreased.
Allowance: Allowance is a special term that is relevant to most fasteners. It is the allotted space or clearing that is put there intentionally between the two threads of the fastener. Thus with allowance, the two threads (the internal thread and the external thread) are separated with a clearance from each other. This is generally used in general manufacturing of steel products. Of course, allowance may not be found on all threads and if it is found on a metric thread then it is named as the fundamental deviation.
Angle Controlled Tightening: This is a procedure that is applied to some fasteners to increase their pre load strength. It is generally used in the automotive industry and composite materials industry. In this process, the fastener is first put under a special torque called snug torque in order to be tightened. Thus this allows the two surfaces which are clamped to tighten on each other. Then in the second phase of this process, the fasteners are given an even more pressurized torque to cause more rotation for further tightening. This process is usually applied to bolts and thus they will need to be ductile in order to survive this. This process is usually applied to bolts that will be used only one time.
Anaerobic Adhesive: This is a special type of an adhesive that is used on various fasteners to create a special medium to lock both the internal and the external thread. Anaerobic adhesive is used in special applications such as composite materials. The anaerobic adhesive becomes hardened when there is no air present that is surrounding it. Thus the adhesive is especially triumphant in situations where there is vacuum, which then bonds the threads together to create an increased tensile strength on the fastener. It is especially used in aerospace and composite material applications.
Annealed: Annealed is a term that is used to denote the state of the fastener. In order to put a fastener in an annealed state, you will have to heat the fastener and once a threshold temperature is reached, then the fastener is cooled down to room temperature conditions. Thus when it is at this state, the fastener will be free of any hardness that might be caused by any sort of heat application. So in the annealed state, the fastener will be soft and it will be in its natural condition. This is used to determine the strength of the fastener under normal conditions.
B
Basic Thread Profile: In order to manufacture fasteners, special care must be given to the threads that comprise it. Threads consist of internal threads and external threads. In a Basic Thread Profile, theoretically, there are no applied torques on the threads. As a result, there are no manufacturing tolerances in a basic thread profile. This is actually the raw state of the threads and from this state various torques are applied and preloaded to create the appropriate fasteners. There is a basic thread profile for all fastener types before they are manufactured in an assembly.
Bolt: Bolt is probably the most common type of fastener around. It is used generally in all types of manufacturing processes from automobiles to airplanes, to even shipbuilding. The manufacturing and the construction industry just would not be possible without the usage of bolts. In essence a bolt is a special type of a threaded fastener. However bolts can not be used separately as they will need to be sued in conjunction with a nut in order to hold the parts together. Bolt must be inserted through a hole that is larger than its diameter in order to successfully fasten the two parts together.
Brinell Hardness Test: This is a special test that is used in the manufacturing of fasteners. The Brinell Hardness Test helps determine the strength of the metallic components and the fasteners by applying a predetermined load to the fastener by using steel ball that has a pre-measured diameter. Thus through this test, the strength and the tensile resistance capacity of the fastener is measured by the amount of the depth of the impression, the steel ball has caused on the material. The Brinell hardness number is quoted with various fasteners to tell its strength for the intended application. Thus greater the Brinell quotient, more powerful will the fastener be.
Bihexagon Head: This is a special type of a fastener that is used in more complex applications. Bihexagon head is generally applied to either bolts or screws. It gets its name from its design. In a bihexagon head, the head and its cross section is designed to be a 12 pointed star. Thus this type of a fastener is used in special applications in which special tools must be used to fasten it. It can be found in the automotive sector as well as in some assembly line of productions.
C
Cadmium Electroplating: Cadmium Electroplating is a special type of coating that is applied onto threaded fasteners. The main purpose of cadmium electroplating is to give the fastener the ability to resist corrosion for prolonged periods of time. Once the fastener is coated with this material, it will give a silverfish appearance to it. It also allows the frictional forces to be reduced on the fastener whenever a torque is applied to it. However there are of course restrictions to cadmium electroplating. You can not use it in environments above 250 C or you can’t use it in situations in which contact or contamination with food is possible.
Class of Fit: Class of Fit is used to designate the measurement of the ability to fit of the two threads. It measures how well the internal threads as well as the external threads mate and also how they fit with each other. Thus the term Class of Fit also measures the fitting quality of the fasteners and it is used to select the fasteners for more complex jobs in various sectors. If it is a Metric thread then it is classified as either coarse, medium or fine depending on its measurement. If it is not a metric thread then the class of fit is classified as 1A, 2A or 3A.
Cleveloc Nut: Cleveloc is a special type of a Nut that is used to create a fastening in which high loads of torque may be applied. Cleveloc Nut is a special fastener that is a registered trade name. It is made completely out of metal and the cleveloc nut is a nut that is torque prevailing. The collar of the cleveloc nut is elliptical rather than circular and thus this provides flexibility in the process of locking. In order to resist higher torques, this special type of a nut is pre-lubricated to reduce the friction on it. In essence it is a flexible locking fastener that is designed to resist higher torques.
Coefficient of Friction: Coefficient of Friction is a number without any measurement dimensions and it is the ratio of the friction forces to the normal forces applied on the fastener. In any case, coefficient of friction is a very powerful number in all cases of manufacturing processes and dynamics as it shows the effect of the friction on the material. The higher the coefficient will mean that the fastener is susceptible to higher loads of friction. In most cases it can be between 0.01 to 0.02 and it’s susceptible to the amount of lubricant that may be used as lubricant will decrease the frictional forces.
Cone Proof Load: This is a special type of a test that is applied to nuts. It measures the refraction resistance of the nut against the pressure that may be applied on it. Cone Proof Load is especially useful in instances to measure the nuts serviceability under high heat conditions. In a cone proof load, axial force is applied to the nut and if the nut fails then it will split itself. Cone Proof Load Test will help measure the detrimental effects of surface discontinuities and its effect on the performance of the nut. In this test, the nut is placed upon a cone shaped testing surface.
Creep: Creep is an important term whenever you are measuring the resistance properties of special type of fasteners such as gaskets. Creep is the term that is used to describe the amount of deformation that takes place whenever the fastener is constantly under load and pressure from its surroundings. Although metal components will usually creep only under high temperature conditions, the amount of creep resistance can be low for gaskets even in room temperature. Thus with fasteners, creep resistance may be quoted with various temperatures to give an idea of the resistance to deformation of the fastener under various conditions.
Commercial Fastener: Commercial Fasteners are special types of fasteners that are not universal in nature, but rather they are fasteners that are manufactured according to the standards of the manufacturers. So instead of conforming to universal standards, they will conform to the requirements of the manufacturer. Sometimes distributors of fasteners may also ask the manufacturers to create fasteners with different dimensions and different types of coating instead of those that are available in the market. Thus although commercial fasteners can’t be used in homogeneous or uniform applications, they will usually pertain more quality compared to generic fasteners. They can be designated with special manufacturer’s code to set them apart.
Commingling: Commingling is a special term that is used in the world of fasteners to describe the process of mixing fasteners that come from different batches. This is deemed as an undesirable situation, although it may be unavoidable in some situations. Now although they may be from different batches, the fasteners (nuts, bolts etc.) will be of same quality, size and grade. Even though they may be of same type and quality, commingling is frowned upon in sectors such as Aerospace and Composite Materials, in which each fastener must be %100 identical to each other. Thus different batches may provide different results on the materials.
D
Dacromet: Dacromet is a special type of coating that is applied to fasteners. It is different from chromium coating as it is designed for more higher performance of the fastener under more extreme conditions. Dacromet is used to provide protection to the metals that are electroplated in the manufacturing process. Dacromet is comprised of using zinc flakes to score on the surface of the fasteners. Depending on the type of the application which the fastener will be used for, the dacromet coating could be of any color. Thus the danger of possible hydrogen embrittlement is avoided by the usage of this coating.
Decompression Point: Decompression Point is a special type of failure criteria that is used on fasteners. It shows the point in which all the combined forces applied on the fastener create a zero pressure point. Thus it is somewhat of a threshold factor that determines the failure of the joint. When the pressures applied on the decompression point exceed the threshold limit, then possibly bolt failure will occur. When the bolts are subjected to higher load and axial pressure, they will start to fret after the decompression point has been passed. Especially after the decompression point has been reached, the load will increase on the load exponentially as failure may occur after that.
Decarburized: Decarburized is a special term that is used to describe the carbon state of the fastener. It is usually used to describe the situation in which the fastener’s core will have higher carbon content compared to the surface of the fastener. Hence a fastener that is said to be decarburized; will have less carbon on its surface then its core. Thus this is a special type of a fastener that can be used in special type of applications. In some situations, it may be desirable for the manufacturer to use decarburized fasteners instead of uniform / homogeneous fasteners.
Direct Tension Indicators: This is a type of a coefficient that is used to measure the amount of the tension that is placed on a fastener. Direct Tension Indicators are usually used in Construction of Buildings and other Civil Engineering Applications. In order to measure the Direct Tension Indicator, the fastener is placed on a special laboratory washer. Then the bolt is placed under tension loads to measure the gap that is left between the fastener and the washer after the load is introduced. If the gap is large then it is presumed that the tension is low, while if the gap is low, then the tension is high on the bolt.
E
Effective Diameter: Effective Diameter is also called the Pitch Diameter and it symbolizes the real effective and functional diameter of the fastener. Effective Diameter is measured by imagining a cylinder that is placed coaxially toward the thread. This imaginary cylinder which is used in measuring the effective diameter has space width and the metal parts equal to each other. Unlike the Virtual Effective Diameter, this dimension symbolizes the real fastening capacity and diameter as a value in all types of measurements related to fasteners.
Embedment: Embedment is a term that is applied to fastener threads or clamped type fasteners. It symbolizes the plastic deformation that is caused by the forces and pressures on the fastener that causes flattening of the surface roughness of the fastener. Thus the joint faces of the fasteners under go plastic deformation on their surface roughness. Unlike other types of deformations, embedment can take place in almost all kinds of situations, as this type of deformation can occur in normal loads and in normal axial pressure. In fact, Embedment can occur even under pressures that are below the loading forces. Thus this term is used as the measure of normal resistance under pressure in fasteners.
Environmentally Assisted Cracking: Sometimes high strength fasteners (made of steel) can experience crackdowns due to environmental conditions. In fact most steel fasteners are designed to take ultra high axial and cranial pressures. However, sometimes these steel fasteners may crack down in a process called “environmentally assisted cracking” and this cracking will occur at a significantly lower pressure levels. One of the main causes of Environmentally Assisted Cracking is caused by hydrogen which is the byproduct of various reactions. One of the most common reactions that lead to by product of hydrogen is corrosion and rusting. Sometimes plating processes can also cause hydrogen to be released in fasteners causing environmentally assisted cracking.
Eccentricity: Eccentricity relates to the symmetry and the axis of fasteners. If any fastener, which has two surfaces (which doesn’t have their axis or centers coincide with each other); then the fastener and its surfaces will be called as eccentric. As long as the center focal points of the two sides are different from each other, then the fastener is definitely eccentric. However the amount of displacement that the centers or the axis have from each other is called eccentricity. In most applications (especially mechanical) the eccentricity should be close to zero.
F
FLURO CARBON THREAD COATING: This is a special type of coating that is applied to threads to cause reduced friction. Thus it is a low friction coating. Fluorocarbon Thread Coating is generally used to coat threaded fasteners before the assembly line undergoes paint. This is an essential type of the painting process as without the Fluorocarbon Thread Coating, the paint particles would stick to the fasteners causing serious fault in the assembly line. Because of the low friction properties, this coating slicks the paint off as the paint can’t stick due to reduced friction. Also this coating can help reduce the scattering that can be caused by torque tension.
Fundamental Deviation: Fundamental Deviation is the clearance that is put there intentionally between the interior thread, exterior thread and the design dimensions of the thread, under maximum metal conditions. Fundamental deviation is expressed in letter format in metric threads. For example, if the metric thread is internal then it is expressed as a Capital Letter, however if the metric thread is external then it is expressed as a small letter. It is also possible to have a zero value for fundamental deviation. In imperial type threads, the fundamental deviation is termed as allowance.
Fatigue Strength: Fatigue Strength is the type of the ability of the fastener (especially screws) to withstand the cyclic pressures that may be put upon them. Applied stress may cause internal stretching on screws and similar fasteners. Thus, if the fastener is subject to the loads continuously, then the fastener will experience material fatigue and it will rupture. In order to determine the fatigue strength of the fastener, it is essential to test it for a specific load under predetermined amount of time. Especially fasteners with greater fatigue strength are used especially in the aeronautics sector and the automotive sector for increased strength of the assembly process.
Finish: Finish is the term that is used to describe the surface of the fasteners especially after they have been applied any form of protective coating etc. In fact, any type of chemical ,organic, and physical treatment of the fastener surface (that results in changed physical properties of the fastener) can be called the Finish. IN addition, any mechanical conditions that relate to the precision or the fineness of the surface of the fastener in any mechanical conditions is also called the finish.
Friction: Friction is an important term in fasteners and in all of mechanics and civil applications. It is the mechanical resistance force between any two surfaces or bodies to their relative movement to each other. The lower the friction rate, the degree of smoothness will be increased in the motion of the fastener. There are two friction coefficients that are used in fasteners, namely Dynamic Friction and Static Friction. For most fasteners, the static friction coefficient will be between 0.01 and 0.02 and in general the static friction forces on a fastener will be much higher than the dynamic friction, but lubricants can lower it considerably.
G
Galling: Galling is the term that is described as the adhesive wear that affects fasteners when they slide across each other in various applications. Galling is a serious event as it can cause the parts of the fastener to break away from the surface after pressure is applied on it. Galling is frequently seen in nuts and bolts when they have zinc coatings or titanium coatings. Galling can occur frequently especially at higher temperatures, thus care must be taken to find fasteners that are correctly coated for the job.
Galvanizing: Galvanizing is the process that occurs on fasteners when the metal parts are coated with zinc. There are various ways in which galvanizing can occur, as it can be done by putting the metal in hot zinc and dipping it or it can also be achieved by electrolysis. In some cases, mechanical deposition may also be used in the galvanizing process. Once the fastener is galvanized, the zinc costing will protect it from various corrosion and the resistance properties of the fastener will be raised considerably. However, sometimes galvanizing the fastener can cause environmental breakdown or galling of the fastener under certain conditions.
Gage: Gage is a special type of an instrument that is used to measure various properties of fasteners. Many different types of measurements of the fasteners can be done with a gage. These measurements may include the effective diameter of the fastener as well as the tensile strength and the axial difference. In some cases, some gages will also measure eccentricity of different types of fasteners.
Grip: Grip is the amount of the thickness of material that fastener can hold onto when it is applied to a surface. In order to measure the grip, the fastener is assembled onto a surface. When the fastener is fastened, the amount of material that it grabs or holds on to can be measured with sensitive instruments. The amount of grip that a fastener has can be very essential in various civil engineering applications in which the fastener must be securely lodged on to secure the structure.
H
Hard Joint: When the bolt is subjected to high compression and axial pressure, then there will be high amount of stiffness in the corresponding joint. In order to achieve a hard joint, the bolt must be rotated with 360 degrees after a full torque is applied to it. Once the bolt is rotated the high compression will cause a hard joint on the corresponding surface. Thus the plates between the nut and bolt will have a hard joint as a result.
Heat Tightening: Heat tightening is a method used on bolts to create more pressure resistant fasteners through heat expansion and coolness contraction. Heat tightening is a method that is used on large bolts to create a more stronger bolt for the application. Also this process can be used to measure the diversification (derivative factor of expansion) under heat. In order to induce heat tightening, the bolt is either heated directly by fire or by using resistance elements. Once the heating is completed up to a certain predetermined degree, then the bolt is allowed to cool down while it is clamped down to create longitudinal contraction.
Hydrogen Embrittlement: Hydrogen Embrittlement is a process that affects steel fasteners. IN most cases, when steel fasteners come into contact with hydrogen, they will lose their integrity and this will cause the faster to fail. Thus hydrogen embrittlement can cause the steel fasteners to fail under sub load of their normal operation. Hydrogen Embrittlement can be caused by the normal corrosion factors that the fastener is subjected to or it can also be caused by electroplating process during manufacturing. Hydrogen Embrittlement is a serious problem as in important civil and mechanic applications; the fastener may rupture or collapse suddenly creating a collapse of the assembly in the process.
High Strength Friction Grip Bolts: High Strength Friction Grip Bolts are special bolts that are used for constructing steel works in steel applications. (They are rarely used in mechanical applications) These special bolts (HSFG) have high tensile strength and high resistance to axial pressure. They must be used with high strength nuts and bolts to have the same loading capacity in the structure. High Strength Friction Grip Bolts are specially tightened to create minimum shank tension, so that they can carry higher transverse loads and pressure.
Hot Bolting: This is a procedure that is performed on fastener (specifically a bolt) when the joints are under load or under pressure. Hot bolting is usually caused by the need for maintenance work even though the joints are under pressure. For example, the replacement of an individual bolt in a civil structure or a mechanic assembly can be considered as hot bolting. Hot bolting is not a technique that should be performed lightly as it can cause irreversible damage to the joint and it can also cause a health hazard for the applicator. Thus this procedure is only done under extreme conditions.
I
Impact Wrench: Impact Wrench is a special type of an automated wrench that gets its power either from electricity or from air. The extra power in the impact wrench allows for the increased torque that can be applied to fasteners for a more better fit with a reduced diameter. The amount of torque that the fastener is subjected to, will be directly influenced by the amount of power that is applied. In addition, the joint stiffness of the fastener will be a part of the process. Impact Wrenches are used in both mechanical and civil applications concerning fasteners.
Integral Fastener: One of the main problems with the fasteners is the fact that most fasteners can loosen or at the least lose their integrity on their hold on the surface, due to internal and external factors that cause vibration. Thus an integral fastener is a specially designed fastener that can withstand the disruptive influence of vibration and thus protect itself from becoming loose. The internal and external threads of integral fasteners may be different then regular fasteners.
Immunize: Many fasteners may have some irregularities on their surface due to the fact that they will have some iron particles or grit, as well as dust particles that can accumulate on their surface. Most of the time, the fineness of the surface of the fastener will be an important issue on the operating performance and the holding / loading capacity of the fastener. Thus, in order to get rid of these iron particles or grit, a special process called immunization is carried out to remove these disruptive particles. Usually in order to achieve this, the fastener is placed under an acidic solution to dissolve the particles and thus to increase the smoothness of the fastener’s surface.
Internal Thread: Internal thread is a thread that is formed in holes. Mostly internal threads are screw threads so that the corresponding screw can be placed upon it for the maximum holding capacity. The internal thread will grab the external thread of the other coupling fastener to create holding power and resistance to axial pressures. Internal threads are more commonly used in nuts to be the conjunction surface of the screw. In addition, these threads will be expressed in diameters or thickness values. This way through the dimension of the thread, the corresponding fastener can be picked out for the maximum smugness.
K
K Factor: K factor is a special type of a factor that is found in the equation T = K * D * F. The formula is an important formula for fasteners as it will give you the approximate torque force that is needed to tighten the fastener under normal operating conditions. K factor is usually a coefficient and it can change from 0,2 to 0,25. The K factor is cited with most fasteners sop that its probable tightening torque can be known by the user. Also in the formula D is the representation of the Fastener Diameter, while F is the loading force on the fastener.
Keps: Keps is a term that is used to describe the joint nut and the washer assembly. Keps comes as pre assembled and the washer along with the nut is connected to each other, so that the nut will not fall off the washer. This is a special type of a fastener assembly that is trademarked to “Shakeproof”. Hence “Kep” is the middle word of the Trademark. Kep is usually bought in large quantities and thus the “s” is added to make the term plural. Hence this special fastener assembly is called Keps
Knurling: In some situations, you may need to create roughened surface on the fastener for variety of reasons. In this case, knurling refers to creating those roughened surfaces on fasteners. Knurling is done by using a special tool called knurl and hence the term knurling. Knurling is performed usually on mechanical applications concerning fasteners.
L
Lock Nut: Lock Nut is a term that is used to describe the situation in which the nut holds on to the adjoining surface or the adjoining fastener. Lock Nut can also be used to describe a nut which is resistant to vibration. Hence normal operating vibration conditions will not loosen the lock nut as it bites into the adjoining surface rather than gripping it. Also additionally in some cases, Lock Nut is used to describe a nut that is in position to lock a nut that is thicker than itself. This is a more common mechanical application, as the lock nut will withstand the loads easing the pressure on the thicker nut thus protecting it in the process.
Left hand Thread: Left hand Thread refers to the thread in a screw. The screw with a left hand thread can only be screwed on to the adjoining surface by rotating the screw counter clockwise (in the opposite direction of the clock movement). Left hand Thread is used in applications that are for special instances, in which the fasteners need to be secured against tampering and also against disruptive external influences such as vibration.
Length of Engagement: Length of Engagement refers to the maximum axial distance in which both the internal thread and the external thread come into contact with each other. In essence, when we are concerned with fasteners, length of engagement signals the amount of gripping power the two threads have against each other. As the length of engagement grows larger, the fasteners are more securely holding on to each other. However the length of engagement can also increase the internal load on the fasteners.
M
Meanshift: Meanshift is the differential in the torque values of the fastener, when the same tightening tool is used on both the soft and the hard joints. The reason why the differences in torques happen is because of the fact that hard joints will have a higher torque than the softer joints. As the mean shift of a tool increases, its ability to create a tighter torque on fasteners is greatly diminished. Thus lower mean shift in a tool will mean higher torque and thus higher tightening power.
Metal to Metal Contact Flange Joint: In a Metal to Metal Contact Flange Joint, the gaskets are pressed upon by the bolts and thus the gasket is under compression which then leads to metal to metal contact. Although metal to metal contact flange joints can be desirable in some situations, it is very hard to measure or calculate the effects of the contact on loading procedures. Unlike other types of joints, Metal to metal contact flange joint can not be tested in a laboratory to give any uniform results for comparison.
Molybdenum Disulphide: Molybdenum Disulphide is a special type of a solid lubricant. It helps to create film of high pressure resistance on the fastener. Molybdenum Disulphide is a very useful type of a solid lubricant as it coats the threads just like a dry lubricant and under adverse temperature conditions, loading conditions and even in the case of hydrogen embrittlement it helps protect the thread. Molybdenum disulphide can also help stabilize the resistance that may be caused by friction.
Maximum Material Condition: Maximum Material Condition is the one of the most fundamental conditions of fasteners. Maximum Material Condition shows the maximum amount of material that is permitted in accordance with the tolerance given to that particular fastener. It can also be shown by the abbreviation MMC.
Milled From Bar Fasteners: Milled from Bar Fasteners are special types of fasteners that are manufactured from special types of machines. Some production techniques for the Milled from Bar Fasteners include the screw machine or the construction of the fastener from the lathe.
N
Nicked Threads: Nicked Threads are indentations or small nicks that occur on the threads of the fasteners. Nicked Threads can be caused by variety of factors as they can be caused during the manufacturing process or during the transport of the fasteners. These nicks can also be termed as gouges in some of the literature. The increase in the diameter of the thread or the fineness of the thread are two important factors that can cause nicked threads.
Nominal Diameter: Nominal Diameter is the external diameter of the thread. Nominal Diameter is a very important dimension in fasteners as it will symbolize the maximal fitting power and the eligible dimensions for most fasteners. Mostly in civil applications, the nominal diameter is cited along with the other dimensions for the fasteners.
Nut Runner: Nut Runner in essence is a tool that is used to tighten fasteners. However one major difference of a nut runner from other tools is the fact that it is torque controlled. Nut runner is usually powered by compressed air to give it the tightening power that it needs. Also another important property that separates the nut runner from the other tools is because of the fact that its design prohibits it being influenced by joint stiffness. Hence a nut runner is more independent in creating a torque on the fastener.
Nyloc Nut: Nyloc Nut is a nut that has a special locking feature for a more tightened grip. This special locking feature is achieved by a nylon insert. Nyloc Nut is a special type of a nut that is used in variety of applications due to the fact that the nylon insert protects the bolt thread against variety of liquids (oil, petroleum substances, water, acids etc.). Nyloc Nut is a patented product by Forest Fasteners.
Nonstandard Fastener: Some fasteners that deviate from the norms are called nonstandard fasteners. In nonstandard fasteners, the width, the length, the height, the surface finish, the coating of the exterior, the diameter of the threads, the eccentricity of the fastener along with its materials and the heating processes that it is subjected to would be different than the published standards. These types of fasteners are usually used for special applications and special assembly lines for different load and resistance values that may be needed. However since they deviate from the published values, the performance of the nonstandard fasteners may sometimes be un documented in laboratories.
O
Octagon Head: Octagon Head is special type of a screw or a bolt that has 8 different sides. Hence it gets the name octagon head. It is usually used in applications that are more oriented toward higher torque pressure and also for applications in which you need to create higher friction torque for the fasteners.
Overtapping: Overtapping is a special procedure that is used to create a more smooth assembly of the internal and external thread by tapping the thread after a plating operation has taken a place. In most situations the internal thread will be tapped more than the external thread for more conformity of the fastener.
Oiled: Oiled is a term that is used on fasteners to demote its condition of being coated with a lubricant substance (not necessarily oil) to protect it from the corrosion and also to decrease its friction coefficient. Thus when a fastener is said to be oiled, it is taught of as protected against corrosion and also reduced in friction.
P
Passivating: Passivating is a special process in which the corrosion resistance on the surface of the fastener is increased by a series of operations. Through this process, a passive film is created on the surface to act as a shield between the fastener and its environment, thus protecting it against corrosion. Passivating is performed on stainless steel fasteners in which the impurities on the surface are washed away by using a nitric acid solution. The fastener is immersed in a nitric acid dip and then it is chemically sprayed to create a corrosion resistant film on the surface of the fastener.
Performance Properties: Performance Properties of a fastener shows its operating conditions and its operating parameters. Performance Properties of a fastener may include such things like the prevailing torque of the fastener, the eccentricity of the fastener, and the locking ability of the fastener. Through these performance properties, the real operating parameters of the fastener can be determined for maximum efficiency in the application.
Pooching: Pooching is a term that describes the effect of the area being raised upwards immediately near tapped hole. Pooching usually takes place due to the tension from the stud. In order to prevent pooching from taking place, the tapped holes that may be present in the beginning threads can be bored outwards, so that they do not become a problem for the fastener.
Polishing: Before the fastener is finished; its surface must be cleansed against irregularities so that it will perform against its expectations. Thus, the process of creating a smoother surface or a finer surface by using mechanical or chemical processes is called polishing. Polishing can be accomplished by creating friction on the surface of the fastener by the use of belts or şt can be accomplished by dipping it into an acidic solution.
Prevailing Torque Nut: Prevailing Torque Nut is a fastener which has a self prevailing torque that can help eliminate natural self loosening of the nut. Prevailing torque nuts can be made out of all metal or they can have nylon inserts inside. In the case of metal nuts with prevailing torque, the upper threads are distorted to create this torque effect. In the case of nylon insert nut s with prevailing torque, there is a polymer type material inside that creates the same torque effect and the loosening is prohibited.
Preload: The tension and the stresses created on a fastener when it is tightened for the first time is called preload. Preload marks the beginning load on a fastener and it is the recommended tension capacity for the fastener. However as the fastener gets under embrittlement, or when it gets corroded or vibrated; the preload capacity of the fastener will decrease considerably.
Proof Properties: Before a fastener is certified as fit for duty, it must be proof tested under various conditions before it can be certified. The Proof Load is the minimum load that the fastener must be able to carry without any fracturing, bending or undergoing plastic deformation. The fastener will then be certified to carry the proof load under any condition. The Proof Properties are the properties that a fastener must be able to perform under a proof test to see that it fulfills all the necessary engineering conditions.
Property Class: Property Class is the system that designates and measures the strength that is present in a nut or a bolt. In metric fasteners, as the property class designation numbers get higher, then the tensile strength of the fastener will increase. For example, a property class of 9 in a fastener will designate the fact that the fastener can withstand 900 MPa of tensile pressure. Thus property class helps designate the fasteners, so that they can be used in their proper category.
Prying: Prying is the process of using leverage against a bolt to create an induced axial pressure. External force applied on the bolt acts as a lever force and thus eccentric axial pressure is produced on the fastener.
Q
Quenching: Quenching is the rapid cooling of the fastener material when it is being manufactured. Quenching allows for a more hardened fastener due to the fact the softness that may be caused by heating is eliminated by the rapid cooling process. There are various types of quenching such as hot quenching, selective quenching and spray quenching.
R
Relaxation: Relaxation is the occurrence of the decrease and the loss in the clamping force that is seen in bolts and other related fasteners. When relaxation occurs, there is no corresponding nut rotation to go along with it. Many studies suggest that relaxation in bolts occur mostly due to external factors such as metal fatigue and metal creep at high temperatures, difference in the thermal expansion properties in the metals, and sometimes due to stress which may cause relaxation in the metal of the fastener.
Rolled Thread: Most threads are formed by cutting into the metal in a designated design. However in rolled threads, the thread is plastically deformed into a blank surface. Rolled Threads are mostly used to create a higher tensile strength in the fastener, as the derivative stresses will be pre – integrated into the thread before loading it. In addition, rolled threads can have a significant positive effect on fatigue reduction and also these types of threads will allow for a better surface finish on the fastener.
Right hand Thread: The threads in screws are said to be Right hand Threads if they are screwed in the clock wise direction. Most of the screws and the corresponding fastener pieces will have a right hand thread as it is the most common way of rolling the thread. Thus the commonality of the right hand thread allows for the uniformity of fastener applications in both mechanical and civil areas.
Rockwell Hardness Test: Rockwell Hardness Test is the test that is performed to measure the hardness of the fastener or its material. In the Rockwell Hardness Test, a steel sphere ball or steel conical shaped object is inserted unto the fastener under pre determined loads. The depth of penetration of the fastener by the steel object will determine the hardness of the fastener. The hardness numbers that are assigned by the Rockwell Hardness test are the measure of the fasteners hardness. Thus as these numbers go up, more the hardness of the fastener will be.
Runout: Runout is a term that is used to describe eccentricity in a fastener. However in some mechanical applications of fasteners, runout can be used to describe the differences in the angularity and the bow of the two surfaces of a fastener. In the case pf a Runout, one component of the fastener will run at a higher torque than the other component in the fastener. Like eccentricity, runout is a condition that is used in special applications of fasteners.
S
Screw: In basic terms, a screw is a fastener with a thread and a head. The screw is the most commonly used fastener today, as it is the main holding tool for the various applications. In most cases, an external threaded nut must be used in conjunction with a screw.
Self Loosening: Self Loosening is the phenomenon in which threaded fasteners can come loose due to internal vibrations etc. Self Loosening can be caused by variety of factors such as embedding, self rotation, stress relaxation and even metal fatigue. When self loosening occurs a bolt may become free of its nut even by internal vibrations alone. This is not a desirable action as it can lead to the fail down of the structural integrity of the fastened application.
Seams: The discontinuities in the fasteners can be called as seams if they are present in the raw material (not on the surface finish, but only on the baseline material) and also if they run longitudinally and not horizontally. Thus seams are separated from fractures as they can be described as the natural fold in the original material. In most mechanical applications, seams will not be welcome on the fastener, although in civil applications it may not be that important.
Sems: Sems is the integrated washer and screw assembly. Thus either a screw or a bolt is captivated by a washer in a Sems Assembly. It was designed with the idea that if the diameter of the screw is greater than the washer hole; then the assembly would hold together even more stronger than before. Thus the item Sems were derived from this new assembly of Pre Assembled washers and screws. Nowadays it is used to describe the washer and the screw assembly.
Shank: Shank is an important term in fastener terminology that expresses the part of the bolt (or any fastener with a head) that is distanced between the head and the most extreme point on the fastener. Thus in most applications, shank is used to describe the usable length of the headed fastener.
Snug Torque: Snug Torque is the torque that is needed to join the both plates together to achieve full metal contact between the two surfaces. Snug Torque is mostly used in applications that need angle control tightening to occur.
Stress Relaxation: Stress relaxation is the reduction of the pressure by the bolt on the joints due to internal factors. Stress relaxation can be caused by creeping, embrittlement, metal fatigue, internal vibrations and also due to high temperature differentials that may occur in the fastener due to its being used in a variety of temperature ranges. Especially when the fastener is subjected to higher loads at higher temperatures, stress relaxation may occur causing integrity failure.
Soft Joint: When the interior material between the nut and the bolt surfaces experience low stiffness then the joint in between the plates is called as the soft joint. If there is a soft joint present, then the bolt must be double tightened with at least two turns to induce a snug state on the fastener surface. Some situations which may cause a soft joint to take place can be things like adding a gasket to the assembly.
Stock Fastener: Some fasteners are used more commonly and in much more greater quantity then regular fasteners. Especially some sizes and some surface qualities in fasteners will be much more preferred over other fasteners. Thus stock fastener is referred to those fasteners that sell in greater quantities and thus it is a fastener that is commercially stocked in most distributors. Hence a stock fastener will also be a popular fastener by the manufacturers.
Structural Bolt: Structural bolt is a very strong and heavy six sided bolt that is used in various civil applications to secure bridges, crossways, and other structures which require powerful fasting procedures for longetivity of the structure. IN structural bolts, there will be a controlled thread length for improved resistance to sheer loads.
Strain Hardening: Strain Hardening is the increase in the hardening of the fastener due to plastic deformations that occur in temperatures that are below re-crystallization range. Thus strain hardening will cause increased strength on the fastener, although it may become more brittle under certain conditions.
T
Taylor Forge Method: Taylor Forge Method is an old method that was formed in the 1930’s which in turn became the basis for A S M E code that is used in the design of flanged joints. The method is registered to the Taylor Forge Engineering Company hence the name Taylor Forge Method. This method is taught to be as overly simplistic today.
Tension Washers: All spring washers or curved washers are called tension washers. One of the main advantages of tension washers is the fact that they produce stiff tension which can be used in spring assemblies. Thus the low stiffness can be a good quality in a fastener when needed.
Thread: Thread is the helical formation on either the internal or the external surface of the fastener. Thus if it is made in a counter clockwise direction (opposite of the clock direction) then it is called a left sides thread. If it is made in a clockwise direction then it is called a right handed thread. Most threaded fasteners will fit much more smugly on to the surface that they are supposed to hold. The Thread Crest is the top part of the thread.
Thread Root: Bottom of any thread is called the Thread Root. Most of the time to reduce fatigue, the thread roots (especially on external threads) will have round ends for higher productivity.
Thread Crest: Thread Crest is the term that describes the top part of the thread. In internal threads, the inner diameter of the thread comprises the thread crest, while on external threads any thread on the outer surface can be considered as the thread crest.
Thread Locker: Threadlocker is the usage of the adhesive products to reduce the vibration and to increase the resistance of the fasteners to vibration. An anaerobic adhesive is applied to the internal or the external threads of the nut and the bolt and once it dries; the thread locker adhesive fills in the empty spaces to create a solid plastic inside with shear and axial resistance. Once the adhesive is hardened, the inner spaces are filled completely.
Tin Electroplating: Tin Electroplating is the method of creating a corrosion resistant on the threaded fastener surface. Tin electroplating is done with mostly tin and with some zinc inside (about %30) to also prevent hydrogen embrittlement. (Zinc increases the strength of the fastener against hydrogen embrittlement). Tin coating can also help with bimetallic corrosion.
Torque: Torque is the rotational moment of the fastener. In most cases, torque is associated with the twisting movement or the twisting load that is exerted on the fastener. Thus as the torque on the fastener is increased, the amount of tensile pressure is also increased in the fastener and as more torque is applied the fastener will be twisted tighter on to the surface. Torque is expressed in Newton – meters in metric fasteners, while in imperial fasteners it is expressed in the dimensions of pounds – feet.
Torque Wrench: Torque wrench is a wrench that has a gauge on it to show the user the amount of torque that is being applied to the fastener. Usually, the Torque Wrench is a manual tool.
Tolerance: The tolerance of a fastener is the permissible deviation from its intended design parameters. Tolerance Grade is the tolerances of a screw thread which is the difference between maximum and minimum metal conditions of the thread.
Toughness: Toughness refers to the fastener’s material’s ability to absorb energy in high amounts that may be caused by variety of pressures or loads. As the toughness of the material increases, the amount of resistance that the fastener will have can increase in the same capacity. However the finishing processes of the fastener may effect the toughness.
Torsion: Torsion is the force that is caused by twisting which is applied on the thread of the fastener. Thus in basic terms, torsion is created by torque.
Tumbling: Tumbling is the procedure of cleaning fasteners or other mechanical parts in a container that is rotating. In tumbling you can add extra cleaning materials to enhance a better finish on the fastener.
U
U Bolt: U Bolt is a special type of a fastener that is shaped like a U. The U bolt is a fastener that is mostly used in the automotive sector as it is generally a fastener that is chosen in the lower parts of the car such as the suspension system. The double ends of the U bolt are threaded giving it a better resistance and loading capacity in suspension systems.
UNC: UNC stands for Unified National Coarse Threads which have 60 degrees flank angle and also have flat crests. UNC Thread is expressed in inches after its standardization in 1948.
UNF: UNF stands for Unified National Fine Threads which have 60 degrees flank angle and also flat crests. However, Unified National Fine Threads have a higher thread diameter compared to United National Coarse Threads.
Unfinished Fastener: Unfinished fastener is a special type of a fastener that resembles the finished product but it has much more wider tolerance factors incorporated in to it. Unfinished Fasteners are generally used for studying the performance properties of standard fasteners under various conditions. An unfinished fastener will have the exact dimensions as the standard fastener but its surface will not be finished (no coating applied etc.)
Ultrasonic Extensometer: Ultrasonic Extensometer is a special instrument that is used to measure the deviation and the change in the length of a fastener as it is being tightened. This instrument used ultrasound waves to give out a precision measurement in the change of the length. It calculates the difference (length deviation) by measuring the length of the fastener before and after the tightening process.
Upsetting: Upsetting is the procedure to increase the cross sectional area of the fastener. Upsetting is done by displacing the manufacturing material of the fastener both longitudinal (vertically along the seams) and also radially (by the diameter of the fastener)
V
Virtual Effective Diameter: Virtual Effective Diameter is the usable effective diameter of a thread. However unlike a real effective diameter, this dimension allows for changes in the flank angle and the pitch angle.
Voids: Any internal fissures that may occur in ferrous materials are called voids. Voids are not something that is desirable in fasteners as the presence of them can endanger the structural integrity of the fastener under high temperature conditions.
W
Washer: Washer is a piece that has a central hole in it. Washer in essence is a part that is assembled between the fastener itself and the surface to which it is being attached to. Washer can perform variety of functions like improved stress distribution on the fastener surface, insulation, and lubrication. The washer face is referred to the bearing surface that is applied on the nut.
Waisted Shank Bolt: Waisted Shank Bolt is a special type of a bolt which has a lower diameter then the minor diameter in the thread. In most cases, waisted shank bolts will have 0.9 times the diameter, compared to the minor diameter.
Wire Thread Insert: Wire Thread Insert is the extra inserted thread to repair tapped holes. A special tool is used to insert these extra threads. Then a special locking compound must be used on the thread, so that it won’t come off when it is subjected to vibration.
Work Hardening: Work Hardening is the plastic deformation of the fastener under certain conditions. Mostly work hardening is caused by the temperature drop under the re crystallization range. Work Hardening can cause increased hardening and increased strengthening of the fastener. It can also be termed as strain hardening in some fasteners.
Y
Yield Controlled Tightening: When a fastener is tightened considerably (so that it would yield) is called yield controlled tightening. Yield controlled tightening can also be called as joint controlled tightening. The angle of rotation present on the fastener is taken as relative to the torque that is applied on the fastener.
Yield Point: Yield Point is the pressure or the stress that is needed to create an elongation in the material of the fastener with a load of less then % 0.5 of the original length of the object. The Yield Point results are expressed in the dimensions of “psi”.
Yield Strength: Yield Strength is the capacity of the fastener material to resist permanent plastic deformation. It is stated as relative to permanent strain as yield strength will have % 0.2 permanent strain resistance capacity.
Z
Zinc Electroplating: Zinc Electroplating is the most widely used method of coating the fastener to protect it against corrosion. In order to conduct zinc electroplating, the fastener is dipped into an acid chloride solution or into an alkaline solution with zinc. Although electroplating is a process that may cause hydrogen embrittlement, the presence of zinc acts as a deterrent.
Zinc Cobalt Alloy Electroplating: Zinc Cobalt Alloy Electroplating is a process that is similar to zinc electroplating and its purpose is to increase the corrosion resistance of the fastener. In Zinc Cobalt Alloy Electroplating, some cobalt is added into the acid chloride mixture to allow for increased plating speed. Generally the amount of cobalt that is added in to the electroplating solution does not exceed %1.
Zinc Phosphate Conversion Coating: Zinc Phosphate Conversion Coating is a secondary process that is performed after zinc electroplating. This type of coating provides a passive film on the fastener surface and thus adds to the fasteners corrosion resistant properties. It is mostly used in bolt threads for maximum protection.