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Glossary

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

Allowance: An intentional difference between the material limits of mating parts, either in the minimum clearance or maximum interference between the parts.

Angularity: The angle between the axes of two fastener surfaces.

Anvil: The part of an installation tool nose assembly used to swage the collar of a lockbolt fastener. Commonly known as a swaging anvil.

Band Anneal or Ban annealing: Induction heat treatment locally applied on a part of the whole of a fastener to increase strength

Bearing Surface: The area that carries load across the face of the material.

Binding Head: One with a rounded top surface, slightly tapered sides and a flat bearing surface, a portion of which may be undercut adjacent to the shank.

Blind Fastener: A fastener that can be placed with access to only one side of an application.

Blind Side: The side of the joint which cannot be accessed (e.g. the inside surface of a tubular or box section).

Body Diameter: The diameter of the unthreaded portion of a threaded shank.

Bolt: An externally threaded fastener that requires a nut to secure the fastened joint.

Boss: Protuberance on a plastic part designed to add strength and/or facilitate fastening or alignment.

BSW - Whitworth Thread: An imperial thread form standard, no longer in mainstream use. It is covered by British Standard BS 84.

Button Head: For threaded fasteners, one with a low, rounded top surface and a large, flat bearing surface.

Case Hardened: Heat treated fastener in which the surface is harder than the core.

Chamfer point: A truncated cone point, the end of which is approximately flat and perpendicular to the fastener axis. On threaded fasteners, chamfer points generally have included angles of 45º to 90º and a point diameter equal to or slightly less than the minor diameter.

Clamp Load: The total load across the joint interface in service. This may vary during service life.

Cold form: Creating components by using forces greater than the material's elastic limit to create extrusions and upsets.

Cone Point: Sharp, conical end of a fastener designed to perforate the application material or align the fastener during assembly.

Countersunk Head: One that is designed to be flush with the surface after installation.

Crack: A clean, crystalline fracture which passes through or across the grain boundaries without inclusion of foreign elements.

Creep: Permanent deformation of a material caused by time, temperature and pressure.

Dog Point: See pilot point

Draft Angle: The amount of slope in the boss hole and/or outside edge, measured from a line perpendicular to the bottom of the boss.

Endurance Limit/ Strength: The maximum alternating stress that a fastener can withstand for a specified number of stress cycles without failure.

Fatigue Strength: The ability of a fastener to resist fracture when subjected to cyclic variations in stress.

Fillers: Inert additives or reinforcements that are added to a polymer to change one or more of its characteristics such as strength or wear resistance.

Fillet/Fillet Radius: Concave junction at two intersecting surfaces of a fastener. Often used to describe the junction between the head and the shank of a threaded fastener (underhead fillet).

Fillister Head: One with a rounded top, cylindrical sides, and flat bearing surface.

Fit: The resulting range of tightness which may occur due to the application of tolerances and allowances in the mating joint members.

Flange: A disc shaped rim formed on the end of a cylindrical object, often related to the head geometry of a fastener or the collar of a lockbolt.

Flank Angle: See thread profile

Flat Head: One with a level surface and a conical bearing surface; available in various nominal head angles.

Flat Trim Head: A flat head with a smaller diameter and lower head height than a standard flat head. TrimFit^® fasteners have this type of head.

Flat Undercut Head: A standard flat head undercut to 70% of the basic head height.

Full Diameter Body/Full-Size Body: an unthreaded portion of a fastener whose diameter is within the dimensional limits of the threaded portion.

Gap Closing: Ability to reduce gape between head and piece part during placing

Gimlet Point: A threaded cone point usually with a point angle of 45º to 50º. It is used on many thread-forming screws.

Grip: The thickness of all of the materials or parts that the fastener is designed to secure when assembled.

Grip Range: The minimum and maximum thickness of all of the materials or parts that the fastener is designed to secure when assembled.

Hardening: Changing the strength characteristics of a fastener through heat treatment or work hardening. See case hardening, induction hardening, and through hardening

Header Point: A chamfered point produced on the blank during the heading operation, before the threads are rolled.

Headform/Head Style: The characteristics of the fastener head. Head styles include large flange, low profile, countersunk, pan, truss, hex, hex flange and socket head.

Head Height:

for a flat surface: the overall distance, measured parallel to the fastener axis, from the top to the bearing surface.

for a conical bearing surface: the overall distance, measured in a line parallel to the fastener axis, from the top to the intersection of the bearing surface with the extended major diameter cylinder on a threaded fastener, or with the shank on an unthreaded fastener.

for flat and oval undercut heads: the 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.

Helix Angle: The angle between the helix of the thread and a line perpendicular to the axis of the screw.

Hexagon Head/Hex Head: One with a flat or indented top surface, six flat sides, and a flat bearing surface.

Hexagon Washer Head/Hex Washer Head: A hex head with an integral, formed washer at the base of the hexagon. The washer diameter may be equal to or greater than the width across the corners.

Hexagon Flange Head/Hex Flange Head: Hex head with a integral circular collar connected to the base of the hexagon by a conic section. Normally, the flanged diameter is larger than the width across the corners of the hexagon.

Hole Size: The size of the opening into which the fastener will be inserted.

Induction Hardened: A heat-treated fastener that has undergone a selective hardening process, using induction coils, to further strengthen a part of the fastener. Camcore^® fasteners undergo this process.

Knurls: Ridges on the exterior surface of a fastener that provide increased torque-to-turn resistance or other performance enhancement. Also called splines or serrations.

Lead-in Chamfer: The tapered end of a fastener which helps ease insertion.

Lead Thread: The thread length from where it starts to where it becomes full size. This distance on machine screws is usually one-half the screw diameter.

Left-Hand Thread: Opposite of standard threads (right-hand threads), receding threads wind in a counter-clockwise direction when the fastener is viewed axially. All left-hand threads are designated LH.

Length of Engagement: The length of full-sized fastener threads that engage in the nut material. The length of the lead thread is not counted in the length of engagement, since its reduced size minimizes any performance benefits. The length of engagement is usually expressed in relationship to the nominal diameter of the screw (e.g. 2 to 2-1/2 diameters of engagement).

Load Flank: For threaded fasteners, the top portion of each thread which applied the preload or load pressure to the mating threads.

Locked Stem: The stem, or mandrel, is locked in the fastener shell during placement. Eliminates the risk of the stem vibrating loose from the rivet head.

Major diameter: The outside or largest diameter of an outside thread.

Maximum Grip: The largest recommended thickness of joint material for a fastener.

Maximum Torque: See ultimate torque.

Minor diameter: The inside or smallest diameter of an external thread.

Nail Point: A sharp, pyramidal end generally having a point angle of 30º to 45º, which is produced by a pinching operation. It is designed for piercing wood and other resilient materials.

Nominal diameter: The major diameter of a screw or, in TRI-ROUNDULAR™ fasteners, the “C" dimension. This designation is used for the purpose of general identification.

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

Oval Head: One with a rounded top surface and a conical bearing surface, with a head angle of nominally 82º (90º for metric).

Oval Point: A radiused point; sometimes referred to as a round point.

Pan Head: One with a flat bearing surface and a flat top surface rounding into a cylindrical side surface. On recessed pan heads, the top surface is semi-ellipitical, rounding into a cylindrical side surface.

Passivation/Passivated: A process to remove contaminants from the surface of stainless steel. Also a name for the chromatic process applied to some metallic finishes to enhance corrosion resistance.

Peak Drive Torque: Amount of force required to pull the members of a joint together; the point at which clamp begins to generate.

Pilot point: A cylindrical point with a diameter somewhat smaller than the shank diameter, which aids alignment and starting during installation. Also called a dog point.

Pitch Cylinder: For threaded fasteners, a cylinder parallel to the fastener axis whose diameter is equidistant between the major and minor diameters.

Pitch Diameter: On straight threads, the diameter of the pitch cylinder.

Point: For threaded fasteners, a conical or cylindrical configuration at the end of the shank on a headed fastener, or each end of a headless fastener. Point types include pilot, gimlet, and nail.

Point Angle: The slope of the end configuration.

Point Diameter: The distance 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 distance measured parallel to the axis of the fastener from the extreme end. It may sometimes be designated as "chamfer length" or "pilot length" on respective point types.

Radial Stress (hoop stress): Forces that propagate from the fastener towards the outside diameter of the joint.

Recess Depth: The distance measured parallel to the fastener axis from the head surface/maximum diameter of the drive system recess to the bottom of that recess.

Reference Dimension: A measurement without tolerance used for informational purposes only.

Right Hand Thread: Standard thread design; winds clockwise in a receding direction.

Rockwell Hardness Test: Test designed to measure the hardness of the fastener, based on an alphanumeric scale. The higher the number, the harder the fastener. Rockwell tests are utilized to test for decarburization and carburization and to determine the amount of resistance to permanent deformation during the testing procedure. They also ensure that heat treating was performed to specification.

Root: The base of the V thread. This is the weakest point on a threaded fastener because it has the smallest cross-sectional area.

Round Head: One with a semi-elliptical top surface and a flat bearing surface. This term is also used to describe a fastener head designed without a driving surface or recess.

Round Washer Head: A round head with an integral washer at its base.

Runout Thread: The thread section that is between the last scratch of thread and the fillet or body.

Sems: Fastener with captivated washer or other secondary element.

Screw: An externally threaded fastener that does not require a nut to secure the fastened joint.

Seam: A narrow, non-crystalline discontinuity, which is usually inherent on the raw material. Seams are usually straight or smooth curved line-discontinuities running parallel to the product axis.

Shank: The portion of a fastener under the head.

Shear: Force that tends to divide an object along a plane parallel to the opposing stresses. Usually measured in lbf/in², psi, MPa or N/m²

Shear Strength: Resistance to tranverse loading. Usually defined as a force in Newtons (N) or pounds (lbf).

Sheet Take-up: See clench.

Socket Head: One with a flat chamfered top surface with a smooth or knurled side surface, and a flat bearing surface. A hexagon or spline (formerly known as “fluted”) socket is formed in the center of the top surface.

Splines: Ridges on the exterior surface of a fastener that provide increased torque-to-turn resistance or other performance enhancement. Also called knurls.

Tail jaws: In Speed Fastening™ tools, the part that grips the mandrel to pull it through the rivet.

Tensile Strength Area: Those used to calculate the tensile strength of an externally threaded fastener, so that the fastener strength is consistent with the material strength. It corrects for the notch and helix effects of the threads, and is a function of the pitch and minor diameters.

Thermoplastic: Polymers characterized by their ductility (fillers may be added to increase stiffness or other characteristics). Thermoplastics can be remelted and reformed several times without degrading the material.

Thermoset: Polymer characterized by extreme stiffness; the initial molding process causes a chemical reaction that "cures" the material, so the resin can not be reprocessed.

Thread Engagement: The amount of thread tooth that is filled by the application material. This measurement is usually expressed as a percentage and is used to determine optimal hole size.

Threaded Fastener: Any screw/bolt (external threads), nut (internal threads), or combination with machine/standard or engineered threads. Does not include custom stamped or formed components with internal and/or external threads.

Threaded Insert: A fastener that provides load-bearing threads in materials too thin or brittle to accept regular standard fasteners.

Thread Profile/Thread Angle: The angle between the flank of the thread and a line perpendicular to the screw axis.

Through Hardened: Heat treated fastener with uniform hardness from the surface to the core.

TIR Approved: A European standard used by the Vehicle Inspectorate — Executive Agency. It is an approved bonding scheme enabling goods vehicles to travel between countries approved by their respective Customs Authorities. The bonding scheme ensures that all load compartments, once sealed (using TIR approved fasteners), cannot have anything added or taken from them without breaking seals or leaving obvious traces of structural damage.

Torque-To-Turn: Typically the torque required to rotate an installed fastener in the application material. Usually used in reference to threaded inserts and clinch fasteners; may also be called Unsupported Torque Resistance.

Torsion: Twisting force applied to a fastener.

Truss Head: One with a rounded top surface and a flat bearing surface; the diameter of the truss head is larger in comparison to the fastener size than the diameter of the corresponding round head.

Ultimate Tensile Stress: The peak longitudal load that can be applied to a fastener, divided by the original cross sectional area. Usually measured in lbf/in², psi, MPa or N/m².

Ultimate Torque: The amount of force at which a threaded fastener begins to strip or otherwise fail in a joint, or strip the threads of an insert or nut. For threaded inserts and clinch fasteners, it may also be referred to as Supported Torque.

UNC (Unified Coarse Thread): An inch thread form (60º) standard defined by ANSI/ASME. Usually used in reference to machine screws. It is covered by ASMEB1.1 and British Standard BS 1580.

Underhead fillet: See fillet

UNF (Unified Fine Thread): An imperial thread form standard defined by ANSI/ASME. Usually used in reference to machine screws. It is covered by ASME B1.1 and British Standard BS 1580.

Washer Face: A circular boss on the bearing surface of a cap screw or nut. The only bolt that has a washer face is the heavy hex structural bolt.

Washer Head: One with a circular collar to provide a large flat bearing surfac (see hex washer head and round washer head for examples).

Wedge Tensile Test: Procedure that induces a bending stress under the head of a bolt, screw or nut, used to demonstrate ductility and the integrity of the head-to-shank junction.

Work Hardening/Cold Working: An increase in metal hardness which is the result of forming processes such as elongation, rolling, heading, etc. This is particularily pronounced in steels, copper and aluminum alloys.

Workpiece: The parts to be riveted.

Yield Strength: Measures the resistance of material to plastic deformation. When a fastener is stretched, yield strength is the point where the fastener will not return to its original length following testing. It is measured in terms of pounds per square inch (psi) or megapascals (MPa). Yield strength is often determined by the offset method illustrated to the left.


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