McGuire Glossary of Fastener Terminology

H - 143 terms

HALAR(R) (ECTRE) (PLASTICS) - Ethlene-chlorotrifluoretlhylene copolymer exhibits better mechanical properties thanmany other fluoroplastics. But like other floroplastics, its flame retardance, chemical resistance and low dielectric constant remain constant over a wide temperature range. These qualities make it suitable for use in such products as electrical insulation, monofilament, tank linings, housings, and electrical components. It may be usefully employed at temperatures from the cryogenic range to about 330F

HALF COLLAR - A reduced-height lockbolt collar used for minimal collar protrusion. Note: will reduce tensile performance.

HALF HEX - A style of blind threaded insert in which the shank has a hex shape for roughly half of the entire part length. The hex portion is adjacent to the head and typically is the same length as the counterbore, followed by a transition to a round shank in the thread area. The hex shank is designed to be installed in a hex hole and offers improved spim-out resistance. The need to orient the part in the mounting hole during installation is generally considered a disadvantage.

HALF SHEARING - Partial penetration piercing, creating a locating button with a height of about 1/2 material thickness.

HALF-DOG POINT - The same as a dog point but half as long; used on short screws for the same purposes as the dog point, but in a shallower hole or slot.

HAMMER - A machine that applies a sharp blow to the work area through the fall of a ram onto an anvil. The ram can be driven by gravity or power.

HAMMER FORGING - The mechanical forming of metal by means of a hammer. The action of the hammer is that of an instantaneous application of pressure in the form of a sudden blow.

HAND FORGING - (1) A forging made by hand on an anvil or under a power hammer without dies containing an exact finishing impression of the part. Such forgings approximate each other in size and shape but do not have the commercial exactness of production die forgings. Used where the quantity of forgings required does not warrant expenditure for special dies, or where the size or shape of the piece is such as to require means other than die forging. (2) A forging worked between flat or simply shaped dies by repeated strokes and manipulation of the piece. Also known as smith forging or flat die forging.

HAND SPRAY - The word spraying generally refers to coating processes that use a spray of particles or droplets to deposit a material onto a substrate. At the substrate surface, the particle droplets form 'splats' or 'platelets' that interlock and build up to give the coating.

HAND STRAIGHTENING - A straightening operation performed on a surface plate to bring a forging within the straightness tolerance. Frequently, a bottom die from a set of finish dies is used instead of a surface plate. Hand tools used include mallets, sledges, blocks jacks, and oil gear presses in addition to regular inspection tools.

HAND TORQUE - 2 TO 5 IN. lbs. initial installation only Removal torque for reference only. Parts to be assembled/disassembled by hand/fingers. NYLOK

HAND TORQUE - 2 to 5 in. lbs initial installation only. Removal torque for reference only. Parts to be assembbled/dissembled by hand/fingers.

HANDLING HOLE - Holes drilled in opposite ends of the die block to permit handling by the use of a crane bar.

HANDLING HOLE - A tapped hole added to tooling components such as cases, hardplates, and fillers to make them easier to lift or insert/remove from the machine or die set.

HANDLING MARKS - Nicks and gouges formed on forgings if improperly handled; most prevalent for forgings in the as-forged condition prior to heat treatment.

HARD CHROMIUM - Chromium plated for engineering rather than decorative applications. Not necessarily harder than the latter.

HARD JOINT - A joint in which the plates and material between the nut and bolt bearing surfaces have a high stiffness when subjected to compression by the bolt load. A joint is usually defined as hard if the bolt is tightened to it full torque and it rotates through an angle of 30 degrees or less after it has been tightened to its snug condition.

HARD METRIC - A term applied to a mounting hole scheme for inserts with metric threads in which the specified mounting hole sizes are in whole millimeter increments.

HARD TOOLING - Tooling made for a specific part.

HARD WELD - A special weldable material that leaves a very hard wear surface. Typically added to transfer fingers.

HARDENABILITY - In ferrous alloy, the property that determines the depth and distribution of hardness induced by quenching. The ability of a steel to harden when cooled from its hardening temperature, as measured by its surface hardness and by the depth of hardening below the surface.

HARDENABILITY - The ability of a steel to form martensite during the quenching process. More simply, a steels ability to become harder and stronger through heat treatment by sacrificing ductility.

HARDENED WASHERS - The force under the head of a bolt or nut can exceed, at high preloads, the compressive yield strength of the clamped material. If this occurs excessive embedding and deformation can result in bolt preload loss. To overcome this, hardened washers under the bolt head can be used to distribute the force over a wider area into the clamped material. A more modern alternative is to use a flange headed nuts and bolts.

HARDENING - A method of heat-treating metals by heating to a temperature within, or above, the critical range, holding at that temperature for a given time, and then cooling rapidly, usually quenching in oil or water.

HARDENING PRECIPITATION - A process of hardening an alloy in which a constituent precipitates from a supersaturated solid solution. Also see Aging.

HARDENING, CASE - A process of surface hardening involving a change in the composition of the outer layer of an iron-base alloy followed by appropriate thermal treatment. Typical case-hardening processes are Carburizing, Cyaniding, Carbonitriding and Nitriding.

HARDENING, FLAME - A process of heating the surface layer of an iron-base alloy above the transformation temperature range by means of a high-temperature flame, followed by quenching.

HARDENING, SECONDARY - An increase in hardness following the normal softening that occurs during tempering of certain alloy steels.

HARDNESS - The resistance of a material to plastic deformation, usually by indention.

HARDNESS & HARDENABILITY - Hardenability is the property of steel that determines the depth and distribution of hardness induced by quenching from the austenitizing temperature. Hardenability should not be confused with hardness as such or with maximum hardness. Hardness is a measure of the ability of a metal to resist penetration as determined by any one of a number of standard tests: (Brinell, Rockwell, Vickers, etc.). The maximum attainable hardness of any steel depends solely on carbon content and is not significantly affected by alloy content. Maximum hardness is realized only when the cooling rate in quenching is rapid enough to ensure full transformation to martensite. The as=quenched surface hardness of a steel part is dependent on carbon content and cooling rate, but the depth to which a certain hardness level is maintained with given quenching conditions is a function of its hardenability. Hardenability is largely determined by the percentage of alloying elements in the steel; however, austenite grain size, time and temperature during austenitizing, and prior microstructure also significantly affect the hardness depth. The hardenability required for a particular part depends on size, design, and service stresses. for highly stressed parts, the best combination of strength and toughness is obtained by through hardening to a martensitic structure followed by adequate tempering. There are applications, however through hardening is not necessary or even.

HARDNESS TESTING - To best determine a material's strength, ease of machinability and wear resistance, one would conduct a resistance-to-penetration hardness test. Rockwell hardness testing is a commonly used scale for indicating the superficial hardness of a material. It is also valuable in helping to make decisions about treatments and coatings. Superficial Rockwell testing is similar- the difference is that it requires smaller minor and major load values.

HARDPLATE - A tooling component located behind a punch or die assembly. It helps to distribute the forming load into the wedge on the heading slide or the faceplate behind the die block.

HARDWARE DEVELOPER - Organization directly responsible for the design, manufacture, analysis, test, and safety compliance documentation of the hardware.

HASTELLOY® - Any one of a group of highly corrosion resistant high strength nickel-based alloys produced and trademarked by Haynes International Inc. Grade include X/C/R and C276

HAYNES® 188/55 - High Temperature Alloy

HEAD - The enlarged shape pre-formed on one end of a headed fastener to provide a bearing surface. (2) A tooling component/feature that is put on a punch or pin in the tooling assembly.

HEAD - (1) A general term derived from forming heads on bolt blanks. The common usage applies to that portion of a part that has been upset and made larger than the starting stock.

HEAD (NAIL ANATOMY) - Round flat metal piece formed at the top of the nail; for increased holding power.

HEAD (Self-Clinching Fasteners) - The head of a self-clinching fastener is often used as a positive stop to determine if the fastener is fully installed. Some clinch fasteners are flush mounted and us the head to displace the panel material. On other type fasteners the function of the head is to prevent the fastener from completely entering the mounting hole in the panel. Heads come in various styles including flat, low profile and countersunk.

HEAD ANGLE - The included angle of the bearing surface of the head.

HEAD CHAMFER - The chamfer at the O.D. or the head, Primarily applied to type S and similar style nuts.

HEAD COUNTERSINK - The countersink on the head end of the part.

HEAD DIAMETER - The diameter at the largest periphery of the head.

HEAD ECCENTRICITY - 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 of 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 - 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 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 fastener having one end enlarged or formed, usually by either cold heading or hot heading processes.

HEADER POINT - A chamfered point normally produced during the heading operation. The screw blank is chamfered before threads are rolled. It is applied to specific screws in certain sizes and lengths.

HEADFORM - The style characteristics of the fastener head. Eg. Low Profile, Large Flange, Countersunk

HEADING - 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.

HEADING - The upsetting of wire, rod, or bar stock in dies to form parts that usually contain portions that are greater in cross-sectional area than the original wire, rod, or bar.

HEADING PUNCH HOLDER - A special 1st station tool holder on a Three-Blow-Two Die Header that allowed the use of upset tooling at the 1st die.

HEADING SLIDE - This is the moving part of the machine that the tooling is mounted on.

HEADLESS FASTENER - A fastener, either threaded or unthreaded, which does not have either end enlarged.

HEAT - A term used to identify the material produced from a single melting operation. Different heats of the same material can vary in chemical composition within prescribed limits. Stock from a single heat will have a consistent analysis and more uniform properties. In the U.K. known as "Cast".

HEAT (FORGING) - Amount of forging stock placed in a batch-type furnace at one time.

HEAT ANALYSIS - A chemical analysis of a given heat by the producer, which determines the percentages of its elements.

HEAT NUMBER/HEAT LOT - This number is generated from the mills that melt the raw material used in nuts, bolt & screws. This number follows the fastener through its life cycle and traces back to the raw material melt source.

HEAT RESISTANCE - This describes the extent to which a bolt retains specified properties as measured by exposure of the material to a certain temperature and environment for a specified time.

HEAT RESISTING STEELS - Those steels which are used for service at relatively high temperatures because they retain much of their strength and resist oxidation under such condition.

HEAT SETTING (SPRING TERM) - Fixturing a spring at an elevated temperature to minimize loss of load at operating temperature.

HEAT STABILIZATION - (Also known as Hot Setting) The process of removing primary creep and inducing beneficial stresses into a spring, so that, when the spring is subjected to an operating stress and temperature. It will exhibit improved stress temperature relaxation properties.

HEAT TIGHTENING - Heat tightening utilises the thermal expansion characteristics of the bolt. The bolt is heated and expands: the nut is indexed (using the angle of turn method) and the system allowed to cool. As the bolt attempts to contract it is constrained longitudinally by the clamped material and a preload results. Methods of heating include direct flame, sheathed heating coil and carbon resistance elements. The process is slow, especially if the strain in the bolt is to be measured, since the system must return to ambient temperature for each measurement. This is not a widely used method and is generally used only on very large bolts.

HEAT TREATING - An operation involving the heating and cooling of a metal to obtain desirable mechanical conditions microstructural or corrosion resistant properties. Any heating or cooling process used to influence the mechanical properties of a metal. In fastener manufacture, it typically refers to the process of austenizing, quenching and tempering a product in order to form a martensitic grain structure (i.e. improve strength properties.)

HEAT TREATMENT - A sequence of controlled heating and cooling operations applied to a solid metal to impart desired properties.

HEAT TREATMENT - A combination of heating and cooling operations applied to a metal or alloy in the solid state to obtain desired conditions or properties. Heating for the sole purpose of hot working is excluded from the meaning of this definition.

HEAT TREATMENT, SOLUTION - A treatment in which an alloy is heated to a suitable temperature and held at this temperature for a sufficient length of time to allow a desired constituent to enter into solid solution, followed by rapid cooling to hold the constituent in solution. The material is then in a supersaturated, unstable state, and may subsequently exhibit Age Hardening.

HEAT-RESISTANT STEEL - Alloy steel designed for application at elevated temperatures.

HEATING, DIFFERENTIAL - A heating process by which the temperature is made to vary throughout the object being heated so that, on cooling, different portions may have such different physical properties as may be desired.

HEATING, INDUCTION - A process of local heating by electrical induction.

HEAVY TORQUE - 3/3 of initial installation value i.e. MIL Spec., plus requirement of removals and clamp load. NYLOK

HEAVY TORQUE - 3/3 of initial installation value i.e. MIL spec., plus requirement of removals and clamp load.

HEIGHT of FUNDAMENTAL TRIANGLE/ V HEIGHT - Thread height that would be present if there were no truncations and both the root and crest had a sharp V profile. The design profile for unified and metric threads has a height of .625 times the height of the fundamental triangle. H denotes this height.

HEIGHT OF THREAD - The distance, measured perpendicular to the axis, between the major and minor cylinders or cones, respectfully.

HEIJUNKA - A production scheduling/leveling tool, essentially use to distribute kanban cards in an efficient manner.

HELICAL - Winding around in a spiral, spring, or coil

HELIX (SEE PITCH) -

HELIX (SPRING TERM) - The spiral form (open or closed) of compression, extension and torsion springs.

HELIX ANGLE - The acute angle between the helix of the thread at the pitch line and the axis of the thread. The helix angle is the compliment of the lead angle.

HELIX ANGLE - The angle of the helix of a helical coil spring

HELIX VARIATION - The variation (measured axially) of the screw thread actual helical path at the pitch cylinder relative to a true helix.

HEM (DUTCH BEND) - Edge of material doubled over onto itself for the purpose of safe handling or to increase edge stiffness.

HEM(DUTCH BEND) - A method of edge conditioning where a portion of the material near the edge is folded onto itself. Hemming is typically used to increase edge stiffness and remove sharp or rough edges.

HEX DRIVE - The hex drive is extremely popular today as it can be turned with an adjustable wrench, combination wrench and 6 or 12 point sockets. The hex drive is better than the square drive for locations where surrounding obstacles limit wrenching access, because smaller wrench-swing arcs can still successfully rotate the fastener.

HEX SOCKET - The Hex Socket screw drive has a hexagonal recess and may be driven by a hex key wrench, also known as as Allen wrench or hex key. Most commonly used on socket screws and socket set screws in either inch or metric standards. A tamper-resistant version includes a pin in the hex recess.

HEX WASHER HEAD SERRATED - Same as an indented hex washer head but with serrations formed into the bearing surface on the underside of the washer. Available slotted or unslotted. Serration geometry is oriented to resist loosing. Also slows the screw at the point of engagement with the mating piece of sheet metal so as to minimize stripping.

HEXAGON HEAD - Flat top surface with hexagonal sides and with a flat bearing surface.

HI-LEAD SCREWS - A power screw series characterized by the use of multiple start threads to produce fastener liner motion than Acme screws. Hi-Lead® screws have a minimum 2 starts and a lead not greater than the diameter of the screw.

HI-TORQUE - Hi-Torque slot drives were designed by Alcoa Fastening Systems, for situations where very high torque is needed, along with the ability to repeatedly install and remove the fastener. The design features curved walls, unlike the straight-walled slot drive. The Type II (Conical/Connie) design adds a conical cup that receives a centering pin on the driver, improving the alignment of the driving tool to the fastener recess.

HIGH STRENGTH FASTENER - A fastener having high tensile and shear strengths attained through combinations of materials, work-hardening, and heat treatment. These fasteners usually have a tensile strength in excess of 120,000 psi.

HIGH STRENGTH FRICTION GRIP BOLTS - (HSFG) Bolts which are of high tensile strength used in conjunction with high strength nuts and hardened steel washers in structural steelwork. The bolts are tightened to a specified minimum shank tension so that transverse loads are transferred across the joint by friction between the plates rather than by shear across the bolt shank.

HIGH TEMPERATURE BOLTS - Bolts specifically manufactured from high temperature alloys to maintain tensile loads at temperatures between 500 degrees F and 1800 degrees F. Example ASTM A193.

HOGOUT - A product machined from bar to plate stock or form a hand forging, rather than from an impression die forging. The process is commonly known as "hogging out" material.

HOLD-DOWN MARKS - Slight indentations or scuff marks on one side of the stock which can result from the pressure of hold down devices during shearing operations.

HOLDING POWER - SET SCREWS - Two setscrews give more holding power than one, but not necessarily twice as much. Holding power is approximately doubled when the second screw is installed in an axial line with the first but is only about 30% greater when the screws are diametrically opposed. Where design dictates that the two screws be installed on the same circumferential line, displacement of 60 degrees is recommended as the best compromise between maximum holding power and minimum metal between tapped holes. This displacement give 1.75 times the holding power of one screw.

HOLE FILL - The ability of a fastener to fill the clearance hole in which it is installed. It is achieved by radial expansion of the fastener body during the installation process.

HOLE ROLLOVER - Rounding of the top edge of a pierced feature caused by the ductility of the metal, which flows in the direction of the applied force.

HOLE-TO-FORM - Distance from the edge of a hole to the inside edge of a formed feature.

HOLE-TO-HOLE - Dimension between the centers of holes.

HOLLOW FORGING - (1) Processes for forging tubes or ring forgings. (2) Cylindrical open die forging, e.g. thick-walled tubes or rings.

HOLLOW RIVET - A rivet with a cavity completely through the shank and the head. Sometimes called Thru hole rivet.

HOMOGENIZING - A high-temperature heat-treatment process intended to eliminate or to decrease chemical segregation by diffusion.

HONE - See LAP.

HOOKE'S LAW - A principle of physics that states that the force needed to extend or compress a spring by some distance is proportional to that distance.

HOOKER EXTRUSION - The following extrusion of a hollow part with a mandrel used to maintain the inside diameter of the extruded part.

HOOKS (SPRING TERM) - The open loops or ends of extension springs.

HOOP STRESS - The tangential stress at each radial element of an insert, case, or sleeve created by the assembly of the insert or sleeve in the case and the radial load applied to the inside of the insert during the forming process.

HOOPSTER - Term used to identify the style of retaining ring with minimal radial projection and shallow groove depth.

HORIZON CURVE - A slight curvature of the head for elegant, professional results. The Finish Ring underneath the head also provides a better finish by cutting the top fibers in the wood for an extra step in counter-sinking.

HOSE CLAMP THREADS - Hose clamp treads are available in a vast range of thread pitches, asymmetrical thread angles with specialty designed thread profile for anti-vibration and capable of withstanding higher pressure of the hoses.

HOSHIN PLANNING - A management policy or strategy deployment approach. A method for establishing goals (and supporting policies) and ensuring that they are the primary focus of the organization.

HOT BOLTING - This term is used for the completion of maintenance work on a bolted joint when the joint is under loading. This can involve the replacement of individual bolts. There are risks both to the joint itself and to health and safety associated with this technique.

HOT DIP GALVANIZING - Immersion of fasteners in a bath of molten zinc for a controlled time to obtain specified coating weight or thickness.

HOT FORGING - Same as hot working - plastically deforming an alloy at a temperature above its recrystallization point, i.e. high enough to avoid strain hardening.

HOT FORMING/FORGING - Working operations such as bending and drawing sheet and plate, forging, pressing, and heading performed on metal heated to temperatures above room temperature. Typically used to produce large diameter fasteners, exotic materials and for small quantity orders of fasteners.

HOT INSPECTION - An in-process examination of forgings, using gauges, templates, or other nondestructive inspection methods to ensure quality.

HOT MELT ADHESIVES - Thermoplastic materials that solidify at room temperature and melt quickly when heated. Excellent bonding strength and fast setting time.

HOT SHORTNESS - Lack of ductility when metal is hot.

HOT TRIMMING - The removal of flash or excess metal from a hot part (such as a forging) in a trimming press.

HOT UPSET FORGING - A bulk forming process for enlarging and reshaping some of the cross-sectional areas of a bar, tube or other product form of uniform (usually round) section. It is accomplished by holding the heated forging stock between grooved dies and applying pressure to the end of the stock, in the direction of its axis, by the use of a heading tool, which spreads (upsets) the end by metal displacement. Also called Hot Heading or Hot Upsetting.

HOT WORKING - The plastic deformation of metal at such a temperature and strain rate that recrystallization takes place simultaneously with the deformation, thus avoiding any strain hardening. Also referred to as hot forging and hot forming. Contrast with cold working.

HOT-DIE FORGING - A process in which dies are heated close to the forging temperature of the alloy being forged; used for difficult-to-forge alloys.

HOT-DIPPED ALUMINIUM - Gives maximum corrosion protection. Dull grayish color. Requires thread size adjustments to permit ease of assembly.

HOT-DIPPED TIN - Silver-gray color. Excellent corrosion, like electroplated tin, but thickness is harder to control. Plating is often used in the food handling industry because it resists organic acids.

HOT-DIPPED ZINC GALVANIZING - Gives maximum corrosion protection. Dull gray in color. Requires thread size adjustments to permit ease of assembly. During the galvanizing process, steel reacts with molten zinc, forming layers of zinc-iron alloy layers which are metallurgically bonded to the steel surface. This hard barrier has a low corrosion rate and resists mechanical damage. Often specified for harsh environments.

HOUSING DIAMETER (DH) - Also referred to as "bore" diameter. This dimension represents the inside diameter of the assembly where an internal retaining ring is installed.

HRB - Rockwell Scale B. B-scale is typically used as a hardness measurement for soft metals (e.g. brass, aluminum, etc.).

HRC - Rockwell Scale C. C-scale is used to measure the hardness of harder metals (e.g. Medium carbon alloy steel).

HRV - Hardness Vickers Scale. Developed as an alternative method to measure the hardness of materials.

HUB - A boss that is in the center of a forging and forms a part of the body of the forging.

HULL CELL - A trapezoidal box of non-conducting material with electrodes arranged to permit observation of cathode or anodic effects over a wide range of current densities.

HYDRAULIC HAMMER - A gravity-drop forging hammer that uses hydraulic pressure to lift the hammer between strokes.

HYDRAULIC PRESS - A forging press with a hydraulically operated ram.

HYDRAULIC TENSIONER - A hydraulic tool used to tighten a fastener by stretching it rather than applying a large torque to the nut. After the fastener has been stretched, the nut is run down the thread to snug up with the joint, the hydraulically applied load is the removed resulting in tension being induced into the fastener.

HYDRO-HONE - Polishing and/or deburring of metallic components by bombarding them with an air-ejected liquid containing fine solid particles in suspension.

HYDRO-PNEUMATIC - Refers to installation tools. The use of an air over oil intensification system to generate the necessary forces required for fastener installation.

HYDROGEN EMBRITTLEMENT - Embrittlement of a metal or alloy caused buy absorption of atomic hydrogen, for example during pickling, cleaning or plating process. Immersion deposit: A metallic deposit produced by a displacement reaction in which one metal displaces another from solution, for example: Fe + Cu2 O Cu +Fe2

HYDROGEN EMBRITTLEMENT - Hydrogen absorption during the electroplating or pickling of carbon steels, which makes gthe spring material brittle and susceptible to cracking. Appropriate post-process heat treatment is essential to minimise the risk of failure.

HYDROGEN EMBRITTLEMENT (Spring Term) - Steel fasteners exposed to hydrogen can fail prematurely at a stress level well below the materials yield strength. Hydrogen embrittlement occurs in fasteners usually because of the part being exposed to hydrogen at some time during its manufacturing process, but it can also occur through in-service corrosion. Electroplating is generally considered to be a major cause of hydrogen absorption in steel fasteners due to the release of hydrogen during the process. Higher strength steels are more susceptible to hydrogen embrittlement than lower strength steels, however it is considered that there is no lower strength limit. As a rule of thumb, steels below Rockwell C 35 area considered to be far less susceptible. Test such as the incremental load hydrogen embrittlement test can be completed to assess if hydrogen embrittlement is present in a batch of fasteners.

HYDROGEN EMBRITTLEMENT RELIEF - ASTM F1941 recommends hydrogen embittlement relief for fasteners of 40 HRC or above. Fasteners are to be baked within 4 hours after electroplating at temperatures of 350 to 450 degress F. Fasteners with a specified maximum hardness of 34 HRC and below have a very low susceptibility to hydrogen embrittlement and do not require baking.

HYSTERESIS - The lagging of the effect behind the cause if the effect. A measure of hysteresis in a spring is represented by the area between the loading and unloading load-deflection curves produced when the spring is stressed within the elastic range.