4. GLOSSARY OF TERMS

Ref (NAVSEA-S9086-CJ-STM-010, 2006)

Term Definition
AARH Arithmetic average roughness height (Ra), is the arithmetic average of the height of the grooves or serrations in the flange of a bolted joint measured from the nominal or ideal surface to the peaks of the serrations, not peak to valley.
Allowance Minimum clearance (positive allowance) or maximum interference (negative allow- ance) between mating parts.
Alloy steel Steel containing significant quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, silicon, sulfur, and phosphorus) added to obtain specific mechanical or physical properties, such as toughness, strength at elevated temperatures, and corrosion-resistance.
Anaerobic thread-locking compound A liquid that solidifies in the absence of air; used to secure threaded fasteners against loosening in service.
Bearing face or surface The surface that is at right angles to the fastener centerline and that bears against thepart or parts that it fastens; the area under the nut or head of a bolt.
Body The unthreaded portion of the shank of an externally threaded fastener.
Body-bound bolt See ″fitted bolt″.
Bolt An externally threaded fastener with an integral, usually hexagonal, head on one end intended to be used with a nut. Sometimes incorrectly called a capscrew.
Bolt stud A headless fastener externally threaded with the same form and fit of thread on both ends or continuously threaded throughout its length. Generally used with a nut on each end.
Bottoming Screwing a capscrew or stud into a tapped hole until it contacts the bottom of the hole. Bottoming should be avoided since it can generate large forces at the contact point, which can crack the material.
Capscrew A threaded fastener with an integral, usually hexagonal, head on one end that is intended for use in a tapped hole. It has stringent controls on its dimensions so that it can be more easily screwed into a tapped hole. (See ″socket head capscrew″).
Chock An equipment mounting interface used between a foundation or sub-base and a piece of equipment to compensate for the inherent minor spacing defects that exist between equipment and their foundations.
Clamping force The force on the mating parts which is created by tightening or preloading a threaded fastener.
Class of thread An alphanumerical (letter and number combination) designation to indicate the standard grade of tolerance and allowance specified for a thread in the inch-based fastener dimensioning system. Neither of the metric-based systems have an equivalent designation, but the metric-based system thread fit tolerance class serves the same function.
Clearance fit A condition between mating, assembled parts that provides a clearance at their maximum dimensional limit. (See “fit”).
Cold heading A room temperature metal forging process using high forces to form a head on bolts and screws. Also called cold forming.
Creep Slow deformation by stress below the normal yield strength, commonly occurring at temperatures above 600 degrees F.
Elastic deformation A change in shape which is fully recoverable if the stress is removed.
Extensometer An instrument used for measuring the extension or stretch of a bolt or stud, such as a micrometer.
Factor of Safety A ratio of a limiting value divided by the force expected during service. For example, the factor of safety for the strength of a bolt is the tensile strength of the bolt divided by the calculated, expected stress the bolt will experience.
Fastener A mechanical device that holds two or more mating parts in definite positions with respect to each other.
Fastener dimensioning system A set of specifications and rules for dimensioning (sizing) fasteners and fastener threads. There are three fastener dimensioning systems commonly used in the US: the inch-based system; the US metric-based system; and the international metric-based system.
Fatigue Failure mechanism which occurs from repeated stresses having a maximum value less than the material tensile strength. A fatigue fracture usually exhibits distinct periods consisting of crack initiation, crack growth and final overload.
Fit A term used to describe the looseness or tightness of two mating parts. The inch-based system uses terms such as Class 1 fit (loose), Class 3 fit (tight), Class 5 fit (interference), thumb press fit (snug).
Fitted bolt A stud or bolt that has been fitted to its mating hole so that the clearances between its unthreaded shank and its mating hole are extremely small. Either the hole is drilled and reamed true and square with the bearing surface and the bolt machined to fit the hole, or the bolt is pre-machined and the hole reamed to fit the bolt. Not to be confused with interference fit.
Forging Forcing metal under pressure into a desired shape usually at elevated temperature.
Functional pitch diameter The pitch diameter of an enveloping thread with perfect pitch, lead, and flank angles and having a specified length of engagement. This diameter includes the cumulative effect of variations in lead (pitch), flank angle, taper, straightness, and roundness. Variations at the thread crest and root are excluded.
Galling A condition on any of the rubbing surfaces of one or both mating parts where friction between microscopic high spots causes localized welding, resulting in spalling, further roughening of the surface, followed by more severe localized welding. This can result in chipping, fragmentation or deformation of the threads or bearing surface.
Grip length The distance from the underside of the head to the end of the full cylindrical portion of the shank including transition threads. It is the nominal screw length minus the basic thread length.
Interference fit A fit between mating assembled parts that provides interference between the internally and externally threaded fasteners at their minimum dimensional limits. Prior to assembly the externally threaded member is larger than the internally threaded member but when assembled become the same size and develop a high prevailing torque.
Internal wrenching bolt A bolt having a large conical head with a flat top, flat bearing surface, and socket or recess, usually hexagon shaped.
Jackbolt A bolt threaded through one piece and bearing against a suitable surface of another piece, so that tightening of the jackbolt will separate the two pieces, as during disassembly of the component. Also, one of a series of bolts threaded through the perimeter of a multi-jackbolt tensioner nut body. When these are torqued, they prestress the main stud. Jackbolts are typically narrow hex head or hex recess bolts.
Ksi Abbreviation for 1,000 pounds per square inch, the k representing 1,000. This is the inch-based system’s unit for pressure and stress.
Length of thread engagement The axial distance that the complete external thread is in contact with the complete internal thread, measured at the pitch diameter.
Mechanically Adjustable Chock A specially designed chock that can be adjusted to various heights by rotating the threaded members. Any planar adjustment is compensated for automatically by a sliding motion of the spherical bearing. The Vibracon Adjustable Chock is one brand of MAC.
Machined threads Threads that are formed by cutting away material.
Major diameter On a straight thread, the major diameter is the diameter of the crest of the external thread or the root of the internal thread. For a taper thread, the major diameter is the diameter of the crest of the external thread or the root of the internal thread measured at any given point along the thread.
Maximum dimensional limit The condition where the crest and root of an externally threaded fastener are at their maximum diameter or the crest and root of an internally threaded fastener are at their minimum diameter.
Minimum dimensional limit The condition where the crest and root of an externally threaded fastener are at their minimum diameter or the crest and root of an internally threaded fastener are at their maximum diameter.
Minor diameter On a straight thread, the minor diameter is the diameter of the root of the external thread or the crest of the internal thread. For a taper thread, the minor diameter is the diameter of the root of the external thread or the crest of the internal thread measured at any given point along the thread.
Multi-jackbolt tensioner (MJBT) or Superbolt Torquenut An assembly consisting of a cylindrical nut body, multiple jackbolts, and a hardened thrust washer. Multi-jackbolt tensioners are pre-loaded by extending the jackbolts, instead of torquing the nut body. Superbolt is one brand of these tensioners.
Nut A nut is an internally threaded fastener, usually with a hexagonal shaped body perpendicular to the internally threaded hole. For self-locking nuts, see ″prevailing torque locknut″.
Peening Peening is the forging of the end of a pin or bolt to expand it. In the case of a bolt or stud, it prevents the nut from coming off.
Pitch The distance, measured parallel to the fastener’s axis, between corresponding points on adjacent thread forms in the same axial plane and on the same side of the axis. In the inch-based fastener dimensioning system, this is usually given in threads per inch. In both metric-based fastener dimensioning systems, this is given in millimeters between adjacent thread crests.
Pitch diameter The diameter of an imaginary cylinder that has a surface that passes through the threads at the point where the width of the thread groove is the same as the width of the thread ridge, roughly half way between the top and bottom of the thread.
Preload The amount of clamping force exerted by a fastener on joined members solely due to tightening the fastener. When a bolt is preloaded the tensile force in the bolt is equal and opposite to the compressive force within the joint members.
Prestress The axial stress in the fastener that results solely from the preload.
Prevailing torque The torque required to rotate a nut or a bolt when the fastener applies no clamping force to the parts being fastened. The prevailing torque must be measured and added to the torque specified to achieve the desired clamping force. The torque required to bring mating parts together is not considered prevailing torque.
Prevailing torque locknut A locknut that maintains a prevailing torque or resistance to rotation even with no clamping force present. Also called a self-locking nut.
Proof load Proof load is a specified test load that a fastener must withstand without indicating any yielding or permanent deformation.
Roll-pin A straight pin made of a tubular section of hardened spring steel slit lengthwise down one side. The pin compresses when driven into a slightly smaller hole and its spring properties retain it in place.
Root diameter The diameter of an imaginary cylinder or cone bounding the bottom of the roots of a screw thread. Root diameter is the more common term for the minor diameter of an external thread or the major diameter of an internal thread
Roll-formed threads Threads formed by forging a smooth rod between rotating or reciprocating dies.
Self-locking threaded fastener A fastener having a self-contained locking feature, such as a strip of polymer, that resists rotation by gripping the mating thread and does not depend upon the bolt, nut, or stud load for locking.
Self-locking nut See ″prevailing torque locknut″.
Shouldering Shouldering occurs when the thread runout at the beginning of the unthreaded shank enters the threaded hole, causing local distortion of the threads and surrounding area.
Slugging A procedure for tightening large fasteners by striking a special wrench, called a slugging wrench, that has a large flat striking surface on the end of its short handle.
Socket head capscrew A headed, externally threaded fastener with a recessed, hexagonal socket for a hex (allen) wrench.
Spalling The breaking or chipping of material, usually by impact forces but also resulting from fatigue and galling.
Spiral-pin A straight pin made of a rolled-up strip of hardened spring steel that looks like a clock spring or spiral in cross section. The pin compresses when driven into a slightly smaller hole and its spring properties retain it in place.
Spring-pin See ″Roll-Pin″ and ″Spiral-Pin″.
Staking The upsetting of the surrounding metal at three or four points with a center punch at the fastener’s head, if it is exposed, to secure the fastener.
Stud A headless fastener threaded on each end or continuously threaded over its entire length. It is intended to be set into a tapped hole either by using a class 5 (interference) fit on the set end or by using an anaerobic thread-locking compound. A stud may have different fits on the set and nut ends.
Tensile strength The maximum tensile stress a material can sustain without tearing apart. Also referred to as ultimate strength. Inch-based fasteners use pounds per square inch (lb/in2 or psi), and sometimes ksi. Metric-based fasteners use mega Pascals (MPa) or Newtons per square millimeter (N/mm2 ).
Tensile stress area The circular cross-sectional area of a theoretical unthreaded rod whose cross-sectional area is such that it would fail in tension at the same load as a particular threaded fastener.
Tensioner nut body On an MJBT, a slender, circular collar internally threaded to fit the main stud or bolt. The collar has integral jackbolts threaded through the perimeter. Torque is only applied to the nut body initially to snug the mating surfaces. See ″Multi-jackbolt tensioner″.
Thread gauges Gauges used to check threads for conformance with specifications. Types of thread gauges include thread-indicating gauge, thread limit gauge, thread plug gauge, thread ring gauge, thread snap gauge, or go/no-go gages.
Thread gauging Using a thread gauge to determine whether a fastener is within specified limits.
Through bolt A bolt that has a head on one end and a nut on the other, which passes completely through the members to be fastened. (See ″bolt″)
Tolerance(s) Tolerances are specified amounts by which dimensions are permitted to vary. The tolerance is the difference between the maximum and the minimum limits permitted.
Tolerance class A dimensionless parameter that defines the fastener thread tolerances for fasteners in both metric-based fastener dimensioning systems.
Torque A turning or twisting force exerted on a fastener. Inch-based fasteners measure torque in foot-pounds (lbf · ft) or inch-pounds (lbf · in), which is equal to the force in pounds applied to the end of a theoretical 1-foot or 1-inch-long wrench handle. Metric based fasteners measure torque in Newton meters (N · m). Conversion factors from U.S. customary units to metric (SI) are: foot pound-force (lbf · ft) to Newton meter (N · m) 1 lbf · ft = 1.356N·minch pound-force (lbf · in) to Newton meter (N · m) 1 lbf · in = 0.113N·m
Torque, breakaway The torque required to start the rotation of a fastener. The magnitude of this torque is significant when checking the bonding of an anaerobic locking compound. The term is also used to describe the torque required to start the rotation of a fastener when loosening it or restarting its rotation when tightening a group of fasteners in successive increments. Breakaway torque will always be higher than that required to continue the rotation.
Torque, prevailing See ″prevailing torque″.
Ultimate strength See ″tensile strength″.
Washerface A shoulder formed on the bearing surface of a bolt head or nut with a smooth bearing surface and a round outer diameter, designed to eliminate the need for a flat washer.
Yield strength The maximum tensile stress that a material can sustain without causing more than a specified amount of permanent deformation. Inch-based fasteners use pounds per square inch (psi) (abbreviated lb/in2 ). Metric-based fasteners use mega Pascals (abbreviated MPa) or Newtons per square millimeter (abbreviated N/mm2 ).

4. GLOSSARY OF TERMS

Ref (NAVSEA-S9086-CJ-STM-010, 2006)

Term Definition
AARH Arithmetic average roughness height (Ra), is the arithmetic average of the height of the grooves or serrations in the flange of a bolted joint measured from the nominal or ideal surface to the peaks of the serrations, not peak to valley.
Allowance Minimum clearance (positive allowance) or maximum interference (negative allow- ance) between mating parts.
Alloy steel Steel containing significant quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, silicon, sulfur, and phosphorus) added to obtain specific mechanical or physical properties, such as toughness, strength at elevated temperatures, and corrosion-resistance.
Anaerobic thread-locking compound A liquid that solidifies in the absence of air; used to secure threaded fasteners against loosening in service.
Bearing face or surface The surface that is at right angles to the fastener centerline and that bears against thepart or parts that it fastens; the area under the nut or head of a bolt.
Body The unthreaded portion of the shank of an externally threaded fastener.
Body-bound bolt See ″fitted bolt″.
Bolt An externally threaded fastener with an integral, usually hexagonal, head on one end intended to be used with a nut. Sometimes incorrectly called a capscrew.
Bolt stud A headless fastener externally threaded with the same form and fit of thread on both ends or continuously threaded throughout its length. Generally used with a nut on each end.
Bottoming Screwing a capscrew or stud into a tapped hole until it contacts the bottom of the hole. Bottoming should be avoided since it can generate large forces at the contact point, which can crack the material.
Capscrew A threaded fastener with an integral, usually hexagonal, head on one end that is intended for use in a tapped hole. It has stringent controls on its dimensions so that it can be more easily screwed into a tapped hole. (See ″socket head capscrew″).
Chock An equipment mounting interface used between a foundation or sub-base and a piece of equipment to compensate for the inherent minor spacing defects that exist between equipment and their foundations.
Clamping force The force on the mating parts which is created by tightening or preloading a threaded fastener.
Class of thread An alphanumerical (letter and number combination) designation to indicate the standard grade of tolerance and allowance specified for a thread in the inch-based fastener dimensioning system. Neither of the metric-based systems have an equivalent designation, but the metric-based system thread fit tolerance class serves the same function.
Clearance fit A condition between mating, assembled parts that provides a clearance at their maximum dimensional limit. (See “fit”).
Cold heading A room temperature metal forging process using high forces to form a head on bolts and screws. Also called cold forming.
Creep Slow deformation by stress below the normal yield strength, commonly occurring at temperatures above 600 degrees F.
Elastic deformation A change in shape which is fully recoverable if the stress is removed.
Extensometer An instrument used for measuring the extension or stretch of a bolt or stud, such as a micrometer.
Factor of Safety A ratio of a limiting value divided by the force expected during service. For example, the factor of safety for the strength of a bolt is the tensile strength of the bolt divided by the calculated, expected stress the bolt will experience.
Fastener A mechanical device that holds two or more mating parts in definite positions with respect to each other.
Fastener dimensioning system A set of specifications and rules for dimensioning (sizing) fasteners and fastener threads. There are three fastener dimensioning systems commonly used in the US: the inch-based system; the US metric-based system; and the international metric-based system.
Fatigue Failure mechanism which occurs from repeated stresses having a maximum value less than the material tensile strength. A fatigue fracture usually exhibits distinct periods consisting of crack initiation, crack growth and final overload.
Fit A term used to describe the looseness or tightness of two mating parts. The inch-based system uses terms such as Class 1 fit (loose), Class 3 fit (tight), Class 5 fit (interference), thumb press fit (snug).
Fitted bolt A stud or bolt that has been fitted to its mating hole so that the clearances between its unthreaded shank and its mating hole are extremely small. Either the hole is drilled and reamed true and square with the bearing surface and the bolt machined to fit the hole, or the bolt is pre-machined and the hole reamed to fit the bolt. Not to be confused with interference fit.
Forging Forcing metal under pressure into a desired shape usually at elevated temperature.
Functional pitch diameter The pitch diameter of an enveloping thread with perfect pitch, lead, and flank angles and having a specified length of engagement. This diameter includes the cumulative effect of variations in lead (pitch), flank angle, taper, straightness, and roundness. Variations at the thread crest and root are excluded.
Galling A condition on any of the rubbing surfaces of one or both mating parts where friction between microscopic high spots causes localized welding, resulting in spalling, further roughening of the surface, followed by more severe localized welding. This can result in chipping, fragmentation or deformation of the threads or bearing surface.
Grip length The distance from the underside of the head to the end of the full cylindrical portion of the shank including transition threads. It is the nominal screw length minus the basic thread length.
Interference fit A fit between mating assembled parts that provides interference between the internally and externally threaded fasteners at their minimum dimensional limits. Prior to assembly the externally threaded member is larger than the internally threaded member but when assembled become the same size and develop a high prevailing torque.
Internal wrenching bolt A bolt having a large conical head with a flat top, flat bearing surface, and socket or recess, usually hexagon shaped.
Jackbolt A bolt threaded through one piece and bearing against a suitable surface of another piece, so that tightening of the jackbolt will separate the two pieces, as during disassembly of the component. Also, one of a series of bolts threaded through the perimeter of a multi-jackbolt tensioner nut body. When these are torqued, they prestress the main stud. Jackbolts are typically narrow hex head or hex recess bolts.
Ksi Abbreviation for 1,000 pounds per square inch, the k representing 1,000. This is the inch-based system’s unit for pressure and stress.
Length of thread engagement The axial distance that the complete external thread is in contact with the complete internal thread, measured at the pitch diameter.
Mechanically Adjustable Chock A specially designed chock that can be adjusted to various heights by rotating the threaded members. Any planar adjustment is compensated for automatically by a sliding motion of the spherical bearing. The Vibracon Adjustable Chock is one brand of MAC.
Machined threads Threads that are formed by cutting away material.
Major diameter On a straight thread, the major diameter is the diameter of the crest of the external thread or the root of the internal thread. For a taper thread, the major diameter is the diameter of the crest of the external thread or the root of the internal thread measured at any given point along the thread.
Maximum dimensional limit The condition where the crest and root of an externally threaded fastener are at their maximum diameter or the crest and root of an internally threaded fastener are at their minimum diameter.
Minimum dimensional limit The condition where the crest and root of an externally threaded fastener are at their minimum diameter or the crest and root of an internally threaded fastener are at their maximum diameter.
Minor diameter On a straight thread, the minor diameter is the diameter of the root of the external thread or the crest of the internal thread. For a taper thread, the minor diameter is the diameter of the root of the external thread or the crest of the internal thread measured at any given point along the thread.
Multi-jackbolt tensioner (MJBT) or Superbolt Torquenut An assembly consisting of a cylindrical nut body, multiple jackbolts, and a hardened thrust washer. Multi-jackbolt tensioners are pre-loaded by extending the jackbolts, instead of torquing the nut body. Superbolt is one brand of these tensioners.
Nut A nut is an internally threaded fastener, usually with a hexagonal shaped body perpendicular to the internally threaded hole. For self-locking nuts, see ″prevailing torque locknut″.
Peening Peening is the forging of the end of a pin or bolt to expand it. In the case of a bolt or stud, it prevents the nut from coming off.
Pitch The distance, measured parallel to the fastener’s axis, between corresponding points on adjacent thread forms in the same axial plane and on the same side of the axis. In the inch-based fastener dimensioning system, this is usually given in threads per inch. In both metric-based fastener dimensioning systems, this is given in millimeters between adjacent thread crests.
Pitch diameter The diameter of an imaginary cylinder that has a surface that passes through the threads at the point where the width of the thread groove is the same as the width of the thread ridge, roughly half way between the top and bottom of the thread.
Preload The amount of clamping force exerted by a fastener on joined members solely due to tightening the fastener. When a bolt is preloaded the tensile force in the bolt is equal and opposite to the compressive force within the joint members.
Prestress The axial stress in the fastener that results solely from the preload.
Prevailing torque The torque required to rotate a nut or a bolt when the fastener applies no clamping force to the parts being fastened. The prevailing torque must be measured and added to the torque specified to achieve the desired clamping force. The torque required to bring mating parts together is not considered prevailing torque.
Prevailing torque locknut A locknut that maintains a prevailing torque or resistance to rotation even with no clamping force present. Also called a self-locking nut.
Proof load Proof load is a specified test load that a fastener must withstand without indicating any yielding or permanent deformation.
Roll-pin A straight pin made of a tubular section of hardened spring steel slit lengthwise down one side. The pin compresses when driven into a slightly smaller hole and its spring properties retain it in place.
Root diameter The diameter of an imaginary cylinder or cone bounding the bottom of the roots of a screw thread. Root diameter is the more common term for the minor diameter of an external thread or the major diameter of an internal thread
Roll-formed threads Threads formed by forging a smooth rod between rotating or reciprocating dies.
Self-locking threaded fastener A fastener having a self-contained locking feature, such as a strip of polymer, that resists rotation by gripping the mating thread and does not depend upon the bolt, nut, or stud load for locking.
Self-locking nut See ″prevailing torque locknut″.
Shouldering Shouldering occurs when the thread runout at the beginning of the unthreaded shank enters the threaded hole, causing local distortion of the threads and surrounding area.
Slugging A procedure for tightening large fasteners by striking a special wrench, called a slugging wrench, that has a large flat striking surface on the end of its short handle.
Socket head capscrew A headed, externally threaded fastener with a recessed, hexagonal socket for a hex (allen) wrench.
Spalling The breaking or chipping of material, usually by impact forces but also resulting from fatigue and galling.
Spiral-pin A straight pin made of a rolled-up strip of hardened spring steel that looks like a clock spring or spiral in cross section. The pin compresses when driven into a slightly smaller hole and its spring properties retain it in place.
Spring-pin See ″Roll-Pin″ and ″Spiral-Pin″.
Staking The upsetting of the surrounding metal at three or four points with a center punch at the fastener’s head, if it is exposed, to secure the fastener.
Stud A headless fastener threaded on each end or continuously threaded over its entire length. It is intended to be set into a tapped hole either by using a class 5 (interference) fit on the set end or by using an anaerobic thread-locking compound. A stud may have different fits on the set and nut ends.
Tensile strength The maximum tensile stress a material can sustain without tearing apart. Also referred to as ultimate strength. Inch-based fasteners use pounds per square inch (lb/in2 or psi), and sometimes ksi. Metric-based fasteners use mega Pascals (MPa) or Newtons per square millimeter (N/mm2 ).
Tensile stress area The circular cross-sectional area of a theoretical unthreaded rod whose cross-sectional area is such that it would fail in tension at the same load as a particular threaded fastener.
Tensioner nut body On an MJBT, a slender, circular collar internally threaded to fit the main stud or bolt. The collar has integral jackbolts threaded through the perimeter. Torque is only applied to the nut body initially to snug the mating surfaces. See ″Multi-jackbolt tensioner″.
Thread gauges Gauges used to check threads for conformance with specifications. Types of thread gauges include thread-indicating gauge, thread limit gauge, thread plug gauge, thread ring gauge, thread snap gauge, or go/no-go gages.
Thread gauging Using a thread gauge to determine whether a fastener is within specified limits.
Through bolt A bolt that has a head on one end and a nut on the other, which passes completely through the members to be fastened. (See ″bolt″)
Tolerance(s) Tolerances are specified amounts by which dimensions are permitted to vary. The tolerance is the difference between the maximum and the minimum limits permitted.
Tolerance class A dimensionless parameter that defines the fastener thread tolerances for fasteners in both metric-based fastener dimensioning systems.
Torque A turning or twisting force exerted on a fastener. Inch-based fasteners measure torque in foot-pounds (lbf · ft) or inch-pounds (lbf · in), which is equal to the force in pounds applied to the end of a theoretical 1-foot or 1-inch-long wrench handle. Metric based fasteners measure torque in Newton meters (N · m). Conversion factors from U.S. customary units to metric (SI) are: foot pound-force (lbf · ft) to Newton meter (N · m) 1 lbf · ft = 1.356N·minch pound-force (lbf · in) to Newton meter (N · m) 1 lbf · in = 0.113N·m
Torque, breakaway The torque required to start the rotation of a fastener. The magnitude of this torque is significant when checking the bonding of an anaerobic locking compound. The term is also used to describe the torque required to start the rotation of a fastener when loosening it or restarting its rotation when tightening a group of fasteners in successive increments. Breakaway torque will always be higher than that required to continue the rotation.
Torque, prevailing See ″prevailing torque″.
Ultimate strength See ″tensile strength″.
Washerface A shoulder formed on the bearing surface of a bolt head or nut with a smooth bearing surface and a round outer diameter, designed to eliminate the need for a flat washer.
Yield strength The maximum tensile stress that a material can sustain without causing more than a specified amount of permanent deformation. Inch-based fasteners use pounds per square inch (psi) (abbreviated lb/in2 ). Metric-based fasteners use mega Pascals (abbreviated MPa) or Newtons per square millimeter (abbreviated N/mm2 ).