Glossary of Fastener Terminology

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

ANSI: The designation of a society of writing specifications. American National Standards Institute, Inc. 25 West 43rd Street, (between 5th and 6th Avenues), 4 floor, New York, NY 10036

ASME: The designation of a society of writing specifications. American Society of Mechanical Engineers United Engineering Center Three Park Avenue, New York, NY 10016-5990

ASTM: The designation of a society for writing specifications American Society for Testing and Materials 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA, 19428-2959 USA

Actual Fit: The actual fit between two mating parts is the relation existing between them with respect to the amount of clearance or interference which is present when they are assembled.

Actual Size: An actual size is a measured size.

Allowance: An allowance is an intentional difference between the maximum material limits of mating parts. It is the minimum clearance (positive allowance) or maximum interference (negative allowance) between such parts.

Alloy Steel: An alloy steel is a steel containing elements other than carbon which have been added to obtain definite mechanical or physical properties, such as higher strength at elevated temperatures, toughness, etc.

Angularity: Angularity is the angle between the axes of two surfaces of a fastener.

Annealed: A fastener is considered in the annealed state when it has been heated and cooled to make it soft-that is, free of hardness caused by working or previous heat treatment.

Anodizing: Anodizing is the formation of an oxide film on the surface by means of an anodic treatment. This is commonly used on aluminum.

 

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Basic Size:
The basic size is that size from which the limits of size are derived by the application of allowances and tolerances.

Bearing Surface: The bearing surface is the supporting or locating surface of a fastener with respect to the part which it fastens (mates). The loading of a fastener is usually through the bearing surface.

Bevel: The angle that one surface or line makes with another when they are not at right angles, and the slant or inclination of such a surface or line.

Blank: A blank is a fastener in some intermediate stage of manufacture.

Body: The body of a threaded fastener is the unthreaded portion of the shank.

Bound Body (Body-Bound or Fitted). A bound body is a body which has a definite interference or extremely small clearance with its mating hole.

Body Diameter. The body diameter s the diameter of the body of a threaded fastener.

Bolt. A bolt is a headed and externally threaded mechanical device designed for insertion through an oversized hole and mated with a nut.

Broaching. Broaching is the process of removing metal by pushing or pulling a cutting tool, called a broach, along the surface.

Burr. A burr is a small amount of material extending out from the edge of a hole, shoulder, etc. as the result of a machining operation.

 

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Carbon Steel:
Carbon steel is a steel which does not contain any substantial amounts of alloying materials other than carbon.

Case Hardened: A case hardened fastener is a fastener of ferrous material having a surface which has been made harder than the core.

Chamfer Angle: The chamfer angle is the angle of the chamfer measured from the normal to the axis of the fastener and is generally specified in conjunction with either a length or a diameter.

Chip: A chip is a small fragment of metal removed from a surface by cutting with a tool.

Coating: Coating is the application of some material such as metal, organic compound, etc. to the surface of a fastener.

Cold Heading Stock: Cold heading stock is material produced under closely controlled manufacturing and inspection methods so as to be suitable for heading and to be free from those defects causing fractures during heading.

Collar: A collar is a raised ring or flange of material on the head or shank of a fastener.

Commercial Fastener: A commercial fastener is a fastener manufactured to published standards and stocked by manufacturers or distributors. The material, dimensions and finish of commercial fasteners conform to the quality level generally recognized by manufacturers and users as commercial quality.

Comparator: A device for inspecting screw threads and outlines by comparing them with a greatly enlarged standard chart.

Compression Fastener: A compression fastener is a fastener the primary function of which is to resist forces which tend to compress it.

Concentric, Concentricity: Two surfaces of a fastener are concentric when they have a common center of axis. Concentricity is the term used to describe this condition.

Counterboring: Counterboring is the process of enlarging for part of its depth a hole previously formed and to provide a shoulder at the bottom of the enlarged hole. Special tools called counterbores are generally used for this operation.

Countersink: A countersink is an internal chamfer.

Countersinking: Countersinking is the process of beveling or flaring the end of a hole. Holes in which countersunk head type fasteners are to be used must be countersunk to provide a mating bearing surface.

Cracks: Fractures passing through or across grain boundaries without the inclusion of foreign elements.

Creep Strength: At elevated temperatures metal under stress elongates. This elongation increased with time and temperature. To prevent failure it is often necessary to change to heat resistant materials.

Crest: That surface of the thread which joins the flanks of the thread and is farthest frdm the cylinder or cone from which the thread projects.

Crest Clearance: As in a thread assembly, the distance, measured perpendicular to the axis, between the crest of a thread and the root of its mating thread.

Cross Drilled: A cross drilled fastener is a fastener having one or more holes in the head or shank at right angles to, and normally intersecting, the axis of the fastener.

Cut Thread: A cut thread is a thread produced by removing material from the surface with a form cutting tool.

 

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Decarburized.
A fastener has a decarburized surface when the carbon content of the surface is lower than the carbon content of the core.

Design Size. The design size is that size from which the limits of size are derived by the application of tolerances. When there is no allowance the design size is the same as the basic size.

Die. (1) One of a pair of hardened metal blocks for forming, impressing, or cutting out a desired shape. (2) (thread). A tool for cutting external threads. Opposite of tap.

Die Chaser. The separate cutting tools used in die heads, which actually cut the screw threads.

Die Fin. A die fin is a slight amount of excess material or flash which may be visible on the bearing surface and/or body of fasteners made by open die heading.

Drilling. Drilling is the process of forming holes by means of specialized cutting tools called drills.

 

 

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Eccentric, Eccentricity:
Two surfaces of a fastener are eccentric when thy do not have the same center or axis. The amount by which the centers or axes are displaced from each other is called eccentricity. This is not to be confused with Total Indicator Reading (TIR).

Electro-Galvanizing: Electro-galvanizing is the process of coating metal with zinc by electroplating.
Elongation. Longitudinal stretching of a fastener caused by a tensile load due either to tightening or to the external load.

Endurance Limit: The endurance limit is the maximum stress that a fastener can withstand without failure for a specified number of stress cycles. (Also called Fatigue Limit.)

Externally Relieved Body: An externally relieved body is a body on which the diameter of the entire body or portion thereof is reduced to less than the rolled thread blank size of the thread.

Extruding: Extruding is the process of reducing the size of some feature or diameter by forcing it through a die.

 

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Facing:
Facing is a machining operation on the end, flat face or shoulder of a fastener.

Fatigue Strength: Under variations in applied stress a fastener feels internal stretching that can cause rupture after a specific number of cycles. The number of cycles to failure for a specific load is the fatigue life of the screw. In rigid assemblies preloading above the external load should eliminate fatigue failure.

Ferrous: Relating to or containing iron.

Fillet: A fillet is the concave junction at two intersecting surfaces of a fastener.

Underhead Fillet: An underhead fillet is the fillet at the junction of the head and shank of a headed fastener.

Fin: A fin is a form of key under the head of a fastener which serves to keep the fastener from turning during assembly and use.

Finish: The term finish is commonly applied to the condition of the surface of a fastener as a result of chemical or organic treatment subsequent to fabrication. The term finish is also applied to some types of fasteners to indicate the condition of the surface as a result of mechanical operations and the degree of precision.

Finish Fastener: A finished fastener is a fastener made to close tolerances and having surfaces other than the threads and bearing surface finished to provide a general high grade appearance.

Fit: Fit is the general term used to signify the range of tightness which may result from the application of a specific combination of allowances and tolerances in the design of mating parts.

Flash: Flash is the thin fin of metal along the sides or around the edges of a forged or upset section. It is caused when metal flows out between the edges of the forging dies.

Flash Plating: Flash plating is a very thin deposit of metal, usually on the order of 0.00005 to 0.0001 5 inch in thickness.

Following Flank: The flank of a thread opposite to the leading flank.

Forging: Forging is the process of forming a product by hammering or pressing. When the material is forged below the re-crystallization temperature it is said to be cold forged. When worked above the re-crystallization temperature it is said to be hot forged.

Form of Thread: The profile of a thread in an axial plane for a length of one pitch.

Full or Nominal Diameter Body: A full or nominal diameter body is a body the diameter of which is generally within the dimensional limits of the major diameter of the thread. Sometimes referred to as “full size body.”

 

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Gage.
An instrument used in the measuring of the important measurements of fasteners.

Galvanizing. Galvanizing is the process of coating metal with zinc by hot dipping, mechanical deposition, or electrolysis.

Gauge. The thickness of sheet metal or the diameter of a wire.

Grains. Grains are the individual crystals of the material.

Grinding. Grinding is the process of removing material from the surface by the cutting action of a bonded abrasive wheel.

Grip. In general, the grip of a fastener is the thickness of material or parts which the fastener is designed to secure when assembled.

Ground Thread. A ground thread is a thread finished on the flanks by a grinding operation.

 

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Hardenability:
In a ferrous alloy, the property that determines the depth and distribution of hardness induced by quenching.

Head: The head of a fastener is the enlarged shape performed on one end of a headed fastener to provide a bearing surface.

Binding Head: The binding head has a rounded top surface, slightly tapered side surface and a flat bearing surface, a portion of which is sometimes undercut adjacent to the shank.

Button Head: A button head as applied to threaded fasteners has a low rounded top surface with a large flat bearing surface.

Fillister Head: The fillister head has a rounded top surface, cylindrical side surface and a flat bearing surface.

Flat Fillister Head: The flat fillister head has a flat top surface, cylindrical side surface and a flat bearing surface.

Head Angle: The head angle is the included angle of the bearing surface of the head.

Head Diameter: The head diameter is the diameter at the largest periphery of the head.

Head Eccentricity: Head eccentricity is the amount that the head of a fastener is eccentric with the fastener body or shank.

Head Height: For a flat bearing surface head, the head height is the overall distance, measured parallel to the fastener axis, from the extreme top to the bearing surface. For a conical bearing surface head, the head height is the overall distance, measured in a line parallel to the fastener axis, from the extreme top to the intersection of the bearing surface with the extended thread major diameter cylinder on a threaded fastener or with the shank on an unthreaded fastener. For flat and oval undercut heads, it is this distance measured to the intersection of the bearing surface with the undercut. For oval heads and undercut oval heads, the overall distance is referred to as total head height.

Head Length: For rectangular or irregular shaped heads, the head length is the distance along the longest axis of the head, measured in a plane perpendicular to the axis of the fastener.

Head Taper: Head taper is the angle formed by the side or sides of the head and the axis of the fastener. This is not applicable to conventional countersunk heads and should not be confused with head angle.

Head Width: The head width is the distance across opposite flats of hexagon, square, or twelve-point heads measured in a plane perpendicular to the fastener axis. For rectangular or irregular shaped heads, the head width is the distance along the narrowest axis of the head measured in a like manner.

Headed Fastener: A headed fastener is a fastener having one end enlarged or pre-formed.

Headless: A headless threaded fastener is a fastener normally having a slot, recess, or socket in one end.

Hexagon Head: The hexagon head has a flat or indented top surface, six flat sides, and a flat bearing surface.

Hexagon Washer Head: The hexagon washer head is a washer head upon which a hexagon head is formed.

Header: A header is a specialized form of press.

Heading: Heading is a manufacturing process involving the use of a header. This process may or may not involve upsetting or extruding. A part made from wire below the recrystallization temperature is said to be cold headed whereas parts made from wire above the recrystallization temperature are said to be hot headed.

Headless Fastener: A headless fastener is a fastener, either threaded or unthreaded which does not have either end enlarged.

High Strength Fastener: A high strength fastener is a fastener having high tensile and shear strengths attained through combinations of materials, work hardening, and heat treatment.

Hot Dip Galvanizing: Hot dip galvanizing is the process of immersing the parts to be coated in a bath of molten zinc.

 

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IFI:
An association of American and Canadian manufacturers of bolts, nuts, rivets, screws, washers and all types of special industrial fasteners and headed parts which play a vital role in the assembly function.

Industrial Fastener Institute
6363 Oak Tree Boulevard

Independence, Ohio 44131

Immunize: To remove small particles of iron or grit from the surface of stainless steel by pickling in an acid solution.

Impact Test: A test to determine the energy absorbed in fracturing a test bar at high velocity. The test may be in tension or in bending, or it may properly be a notch test if a notch is present, creating multi- axial stresses.

Inclusions: Inclusions are particles of non-metallic impurities contained in material.

Internally Relieved Body: An internally relieved body is a body which has an axial hole drilled through a portion of the body.

 

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Knurling:
Knurling is the process of producing a roughened surface by means of a specialized forming tool called a knurl.

 

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Laps:
Laps are surface defects caused by folding over fins or sharp corners into the surface of the material.

Length: The length of a headed fastener is the distance from the intersection of the largest diameter of the head with the bearing surface to the extreme point, measured in a line parallel to the axis of the fastener. Exceptions: The length of a shoulder screw and a socket head shoulder screw is the length of the shoulder. The length of a flat top countersunk head tubular rivet with chamfered top) is measured from the intersection of the bearing surface with the shank diameter to the extreme point. The length of a headless fastener is the distance from one extreme point to the other, measured in a line parallel to the axis of the fastener.

 

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Machining:
Machining is the process of forming the surface by cutting away material.

Malleable: A commercial iron that is capable of being extended or shaped by beating with a hammer or by the pressure of rollers.

Maximum Material Condition: The maximum material condition of a feature of a fastener means the maximum amount of material permitted by the tolerance shown for that feature (abbreviated MMC).

Mechanical Galvanizing: Mechanical galvanizing is a process in which powdered zinc is applied to a base metal using the principles of cold welding and barrel finishing techniques.

Mechanical Properties: Mechanical properties are those properties which involve a relationship between strain and stress. Hardness, proof load, yield strength and ultimate tensile strength are examples of mechanical properties. The final combination of the fastener’s mechanical properties gained during its manufacture. and post-treatment processing.

Milled From Bar: Milled from bar fasteners are fasteners machined from bar stock on a lathe, screw machine, etc.

 

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Neck:
Neck is used to define: (1) a specialized form of a portion of the body of fasteners near the head to perform a definite function, such as preventing rotation, etc.: and (2) a reduced diameter of a portion of the shank of a fastener which is required for design or manufacturing reasons. Various neck styles are fin neck, ribbed neck and square neck.

Nitriding: A surface hardening process used on ferrous metals by heating the metal in contact with ammonia gas or other nitrogenous material.

Nominal Size: the nominal size is the designation used for the purpose of general identification.
Non-Ferrous Metal. Metals or alloys without an appreciable amount of iron. Examples are aluminum, brass, copper, etc.

Nonstandard Fastener: A nonstandard fastener is a fastener which differs in size, length, material, or finish from established and published standards.

Normalize: To remove internal stresses by heating a metal piece to its critical temperature and allowing it to cool very slowly.

Nut Thickness: Nut thickness is the overall distance from the top of the nut to the bearing surface, measured parallel to the axis of the nut.

Nut Width and Length: the nut width is the distance across opposite flats of hexagon, square or twelve-point nuts.

 

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Oiled:
Oiled is the term denoting the application of a suitable corrosion retarding oil to a fastener.

 

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Passivating:
Passivating is the process of dissolving ferrous particles and surface impurities from stainless steel by chemical means (normally a nitric acid dip) and to produce a passive film on the surface. The purpose is to improve the corrosion resistance of the surface.

Physical Properties: Physical properties are the properties defining the basic characteristics of the material or fastener, They are inherent in the raw material and remain basically unchanged in the fastener following its manufacture and include: density, coefficient of thermal expansion, electrical conductivity, thermal conductivity and magnetic properties.

Performance Properties: Functional design features manufactured into the fastener to satisfy various requirements of the service application such as locking ability, prevailing torque, etc.

Pickling: Pickling is the process of removing surface oxides or impurities by chemical or electrochemical means.

Pin: A pin is a straight cylindrical or tapered fastener, with or without a head, designed to perform a semipermanent attaching or locating function.

Pitch: The distance; measured parallel to fastener axis, between corresponding points on adjacent thread forms in the same axial plane and on the same side of the axis.

Pitch Diameter: On a straight thread, the diameter of the coaxial cylinder, the surface of which would pass through the thread profiles at such points as to make the width of the groove equal to one-half of the basic pitch. On a perfect thread this occurs at the point where the widths of the thread and groove are equal.

Pits: Pits are sharp depressions on the surface of a raw material or fastener.

Plain: Plain as applied to finish of fasteners is used to indicate that the fastener has had no supplementary surface treatment, such as plating, coating, etc., other than being oiled.

Plating: Plating is the application of a metallic deposit on the surface of the fastener by electrolysis, impact, or other suitable means.

Plating Build Up: Plating build up is the term used to describe the disposition of more plating on edges or corners than on the other surfaces of the fasteners.

Point: The point of a fastener is the configuration of the end of the shank of a headed fastener or of each end of a headless fastener. Points of fasteners fall into the general categories described and illustrated below:

Chamfer Point: A chamfer point is a truncated cone point, the end of which is approximately flat and perpendicular to the fastener axis. These points on threaded fasteners generally have point included angles of 45 to 90 degrees and a point diameter equal to or slightly less than the minor diameter of the thread. This point is intended to facilitate entry of fasteners into holes at assemble.

Cone Point: A cone point is a sharp conical point designed to perform perforating or aligning functions at assembly.

Gimlet point: A gimlet point is a threaded cone point usually have a point angle of 45 to 50 degrees. It is used on thread forming screws such a Type “A” tapping screws, wood screws, lag bolts, etc.

Oval Point: An oval point is a radiused point, sometimes referred to as a ‘Crowned End’ or “Round Point.”

Point Diameter: The point diameter is the diameter of the point measured at the extreme end of the fastener. It may sometimes be designated as “Chamfer Diameter” or ‘Pilot Diameter” on respective point types.

Point Length: the point length is the length of the pointed portion of the fastener, measured parallel to the axis of the fastener from the extreme end. It may sometimes be designated a “Chamfer Length” or Pilot Length” on respective point types.

Point Radius: The point radius is the spherical radius on an oval or spherical point.

Plain Point: The term plain point is applied to the end of a fastener cut approximately flat and perpendicular to the fastener axis. These points on threaded fasteners may be slightly concave especially when threads are rolled.

Spherical Point. A spherical point is an oval point in which the point radius is equal to half the shank diameter.

Pointing: Pointing is a secondary machining operation consisting of cutting points on fastener blanks which were not pointed during the heading operation.

Polishing: Polishing is the process of producing a smooth surface by rubbing with fine abrasive wheels, belts, or compounds.

Position tolerance: The axis of the feature shall fall within or pass through the zone bounded by a circle about the true position or reference axis whose diameter is the position tolerance.

Precision: Precision is the result of being manufactured to close tolerances.

Proof Load: A proof load is a specified test load which a tastener must withstand without any indication of failure.

Proof Test: A proof test is any specified test required for a fastener to indicate that it is suitable for the purpose intended.

Punching: Punching is the process of trimming or removing material with dies in a press.

 

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Quench Hardening.
Hardening a ferrous alloy by austenitizing and then cooling rapidly enough so that some or all of the austenite transforms to martensite.

Quenching: Rapid cooling. When applicable, the following more specific terms should be used; direct quenching, fog quenching, hot quenching, interrupted quenching, selective quenching, spray quenching, and time quenching.

 

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Ream:
To finish a drilled or punched hole very accurately with a rotating fluted tool of the required diameter.

Reamer: Tool used for enlarging holes previously formed by drilling or boring.

Recess Depth: The the distance measured parallel to the fastener axis from the intersection of the head surface with the maximum diameter of the recess to the bottom of the recess.

Recess Diameter. The recess diameter is the diameter measured in a plane perpendicular to the axis of the fastener over the intersection of the outermost extremities of the recess with the head surface.

Recess Eccentricity: Recess eccentricity is the amount that a recess in a recessed head is eccentric with the shank of the fastener.

Recess Width: The recess width is the distance measured in a plane perpendicular to the axis of the fastener across the intersection of the sides or wings of the recess with the head surface.

Recessed Head: A recessed head is a head having a specially formed indentation or recess centered in its top surface.

Reduced Diameter Body: A reduced diameter body is a body the diameter of which may range from the rolled thread blank size to the minimum major diameter of the thread and is common on screws having rolled threads. Sometimes referred to as undersize body,’ a term which is not recommended.

Reference Dimension: A reference dimension on a fastener is a dimension without tolerance used for information purposes only.

Relief: The amount one plane surface of a piece is set below or above another plane, usually for clearance or for economy in machining.

Rib: Ribs are small ridges of material usually formed longitudinally around the shank.

Rivet: A rivet is a headed metal fastener of malleable material used to join parts of structures and machines by inserting the shanks through the aligned hole in each piece and forming a head on the headless end by upsetting.

Rockwell Hardness Test: A measure of hardness by determining the depth of penetration of a penetrator into the specimen under certain fixed conditions of test. The penetrator may be either a steel ball or a diamond sphero-conical penetrator. The hardness number is related to the depth of the indentation and the higher the number the harder the material.

Rolled Thread: A rolled thread is a thread produced by the action of a form tool which when pressed into the surface of a blank displaces material radially.

Runout: Runout is a term frequently used interchangeably with eccentricity but which normally refers to the amount which the outside surface of one component of a fastener runs out with respect to the outside surface of another component. As such, it includes eccentricity, angularity and bow. The amount of runout is usually expressed in terms of Total Indicator Reading (TIR) or Full Indicator Reading (FIR). .

 

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Scale:
Scale is an oxide of iron sometimes formed on the surfaces of hot headed or forged fasteners.

Screw Stock: Screw stock is metal in the form of wire or rod which is used for making screw machine parts. Usually it is of a free machining type of material.

Seams: Inherent discontinuities in a raw material that run longitudinally. They are folds in the material, not fractures at the grain boundary.

Semi-Finished Fastener: A semi-finished fastener is a fastener made to the same basic dimensions as a finished fastener but having greater tolerances on most dimensions and only the bearing surface and threads finished.

Shank: The shank is that portion of a headed fastener which lies between the head and the extreme point.

Shank Diameter: The shank diameter is the diameter of the shank of an unthreaded fastener. The diameter of the unthreaded portion of a threaded shank is termed the Body Diameter.

Shank Length: Shank length is the length of shank, measured parallel to the axis of the fastener.

Shaving: Shaving is a cutting operation in which thin layers of material are removed from the outer surfaces of the product.

Shear Fastener: A shear fastener is a fastener whose primary function is to resist forces which tend to shear it.

Shoulder: A shoulder is an enlarged portion of the body of a threaded fastener or shank of an unthreaded fastener.

Sliver: A sliver is an irregular shaped piece of metal clinging loosely to the finished fastener.

Slot Depth: The slot depth on a headed fastener is the distance measured parallel to the axis of the fastener from the highest part of the head to the intersection of the bottom of the slot with the head or bearing surface. The slot depth on a nut or headless fastener is the distance measured parallel to the fastener axis from the top surface to the extreme bottom of the slot.

Slot Eccentricity: Slot eccentricity is the amount that a slot in a slotted head is eccentric with the body of the fastener.

Slot Width: The slot width is the distance measured in a plane perpendicular to the axis of the fastener over the intersection of the sides of the slot with the head surface of a headed fastener or top surface of a nut.

Slotting: Slotting is the process of forming or cutting the slot on the head of a fastener during either the primary or secondary operation.

Socket Depth: the socket depth is the distance measured parallel to the fastener axis from the intersection of the socket with the head surface to the extreme end of the socket. In socket head screws, the effective socket depth is most often specified as “Key Engagement’ which is the distance from the intersection of the socket with the head surface to that depth to which the key or wrench will penetrate, measured in a like manner.

Socket Diameter: the socket diameter is the diameter measured in a plane. perpendicular to the axis of the fastener over the intersection of the outermost extremities of the socket with the head surface.

Socket Width: The socket width is the distance measured in a plane perpendicular to the axis of the fastener over the intersection of opposite sides of the socket with the head surface.

Soft: Soft describes the condition of a fastener which, though made from a material which can be, and normally is, hardened by heat treatment, has been left in the as-fabricated temper.

Special Fastener: A special fastener is a fastener which differs in any respect from recognized standards.

Stainless steel: Stainless steel is a corrosion resistant type of alloy steel which contains a minimum of 12 percent chromium.

Standard Fastener: A standard fastener is a fastener which conforms in all respects to recognized standards.

Stock Fastener: A stock fastener is a fastener which is commercially stocked in quantity by manufacturers or distributors of fasteners.

Strain Hardening: Strain hardening is the increase in hardness, and hence strength, resulting from plastic deformation at a temperature below the re-crystallization range. Sometimes called “work hardening.”

Stress Area: Theoretical area in the thread section of a fastener over which the load is applied.

Stud: A stud is a fastener with no head, which has threads at both ends of the shank. Like a screw, one end is inserted into an internally tapped hole and tension is induced by tightening a nut on the other end. If a stud is threaded its entire length and a nut is used on both ends to create tension, it serves the function of a bolt and is then classified as a stud bolt.

Surface Treatment: Surface treatment is any treatment which changes the chemical, physical, or mechanical properties of a surface.

 

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Taper:
Taper, as used for fasteners, is the angle between one side and the axis of the fastener. taper may refer to head, shank, or some other feature of a fastener.

Temper: Temper is the state of a metal or alloy involving its structure and mechanical properties. Temper varies from the annealed temper (soft) to spring temper.

Tensile Strength: Force or stress required to break a fastener when pulled in straight tension. When expressed as a force, lbs., it applies to a specific size part. Expressed as a stress, psi, means the force is applied over a specific area and it could apply to a range of sizes. For example, socket screws from No. 0 to 1/2 inch can withstand an applied stress of 180,000 psi.

Tension Fastener: A tension fastener is a fastener whose primary function is to resist forces which tend to elongate it.

Thread: A thread is a ridge of uniform section in the form of a helix on the external or internal surface of a cylinder. This is known as a straight or parallel thread to distinguish it from a taper thread which is formed on a cone.

Complete Thread: The length of complete thread is the length of that cross section of a threaded length having full form at both crest and root. Where there is a chamfer at the start of the thread not exceeding two pitches in length, it is included within the length of the complete thread. The thread length on the drawing shall be the gaging length or the length of threads having full form. i.e., the partial threads shall be outside or beyond the length specified.

When designing threaded products, it is necessary to take cognizance of: (1) such permissible length of chamfer and (2) the first two threads which by virtue of Hl-L0 gaging practice may exceed the product limits and which may be included within the length of complete thread. However, where the application is such as to require a minimumor maximum number, or length, of complete threads the specification shall so state. Similar specification is required for definite length of engagement.

Effective Thread: the effective (or useful) thread includes the complete thread and that portion of the incomplete thread having fully formed roots but having crests not fully formed.

Incomplete Thread: this is also known as the vanish or washout thread. On straight threads, the incomplete thread is that portion at the end having roots not fully formed by the lead or chamfer on threading tools.

On taler threads, the crest at the end may also be not fully formed due to the intersection of the major cone of an external thread or the minor cone of an internal thread with the cylindrical surface of the work.

Left-Hand Thread: A thread is a left-hand thread if, when viewed axially, it winds in a counterclockwise and receding direction, All left-hand threads are designated LH.

Right-Hand Thread: A thread is a right-hand thread if, when viewed axially, it winds in a clockwise and receding direction. All threads are right-hand threads unless otherwise designated.

Total Thread: The total thread includes the complete or effective thread and the incomplete thread.
Threaded Fastener. A threaded fastener is a fastener a portion of which has some form of screw thread.

Tolerance: a tolerance is the total permissible variation of a size: The tolerance is the difference between the limits of size.

Torsion: Twisting force applied to a fastener during tightening.

Toughness: Toughness is the ability of a material to absorb considerable energy without fracturing.

Trimming: Trimming is the term applied to the process of shaping or sizing by forcing a part through a die of desired size and shape.

Tumbling: Tumbling is the process of cleaning or abrading parts in a rotating container, either with or without cleaning or abrasive materials.

 

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UNC:
The designation describing Unified National Coarse threads.

UNF: The designation describing Unified National Fine threads.

Unfinished Fastener: An unfinished fastener is a fastener made to the same basic dimensions as a finished fastener but having relatively wider tolerances than a finished fastener and having all surfaces in their formed condition.

Upsetting: Upsetting is the process of increasing the cross sectional area by displacement of material longitudinally and radially.

 

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Voids:
Voids are internal fissures in ferrous material. They are sometimes called ‘chrome checks,” “fish eyes,” “shatter cracks” and “snowflakes.”

 

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Washer:
A washer is a part usually thin, having a centrally located hole or partial slot. The washer performs various functions when assembled between the bearing surface of a fastener and the part being attached. Insulation, lubrication, spanning of large clearance holes, and improved stress distribution are a few design uses.

Washer Face: A washer face is a circular boss on the bearing surface of a bolt or nut.

Width Across Corners: The width across corners of hexagon, square, or rectangular shaped fasteners is the distance measured perpendicular to the axis of the fastener from the intersection of two sides to the intersection of the two opposite sides.

Width Across Flats: The width across flats of hexagon or square heads of fasteners is the distance measured perpendicular to the fastener axis across opposite sides of the fastener.

Work Hardening: Work hardening is the increase in hardness, and hence strength, resulting from plastic deformation at a temperature below the re-crystallization range. Sometimes called Strain Hardening.

 

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Yield Point.
The stress necessary to produce an elongation under load of 0.50 percent of the specimen’s original length. Expressed as psi.

Yield Strength. This is the measure of the resistance of a material to plastic (permanent) deformation. It is usually at a point of 0.2% permanent strain.

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