McGuire Glossary of Fastener Terminology

F - 203 terms

FACE - In screw machine work the operation of removing material from the out ed of the part.

FACE ANGLE - This is the angle on the nose of a punch or pin measured from a line perpendicular to the axis of the punch or pin.

FACE STEP - In type FH studs the cylindrical step between the ribs which is used to control the roundness of the head.

FACE-CENTERED CUBIC STRUCTURE (FCC) - A cubic structure found in steel. Refers to the arrangement of atoms within the metals structure. Steel in this state has low magnetic permeability. Atomically, lattice points are positioned on the faces of the cube of which each unit cube gets exactly one-half contribution, in addition to the corner lattice.

FACING - The machining operation on the end, flat face, or shoulder of a fastener.

FACTOR OF SAFETY - A multiplying factor to be applied to limit loads for purposes of analytical assessment (design factor) or test verification (test factor) of design adequacy in strength or stability.

FAILURE - Rupture, collapse, excessive deformation, or any other phenomenon resulting in the inability of a structure to sustain specified loads, pressures, and environments or to function as designed.

FAILURE MODE - A description of the way the fastener failure occurred.

FAST START TIP - With the sharp threads all the way t the tip, this fastener has an immediate grip for a fast start. The inset thread cut drastically reduces splitting effect and minimizes the driving torque needed to engage the wood.

FASTENER - A mechanical device for holding two or more bodies in definite positions with respect to each other.

FASTENER - For purposes of the NASA Technical Standard, a bolt or a screw that joins two or more parts and transfers load between them!

FASTENER BODY - The section of the fastener, excluding the head, which is generally the functioning/expanding part in contact with the joint on blind rivets.

FASTENER HARDNESS - The measure to approximate the strength of a fastener. Usually measured in the Rockwell or Rockwell Superficial Scales.

FASTENER INDENTIFICATION MARKING - A stamp, paint, or other permanent identifier that may include manufacturer information and applicable grade markings for certification purposes.

FASTENER QUALITY - The accuracy of manufacture of the fastener such that it conforms to its specified dimensional tolerances, mechanical properties, limits, and other requirements stated under applicable standards.

FASTENER SPECIFICATIONS - A precise statement of set requirements to be satisfied by a fastener, its material, or its processing. It also indicates the procedure used to determine whether the requirements given are satisfied. This would include specifications from various standards organizations, i.e. ASTM, ANSI

FASTENER STANDARD - A document which details the attributes of a finished fastener and includes such characteristics as geometry, material or chemistry, heat treatment, finish, testing lot size, and packaging.

FASTENER TESTING - A determination or verification that the fastener meets it specifications requirements.

FASTENOMICS - Fastener training aids: McGuire Glossary of Fastener Terminology and THE Fastener Quiz.

FATIGUE - The cumulative irreversible damage incurred in materials caused by cyclic application of stresses and environments, resulting in degradation of load carrying capability.

FATIGUE - A phenomenon giving rise to a type of failure which takes place under conditions involving repeated or fluctuating stresses below the elastic limit of the material.

FATIGUE LIFE - The length of time a thread lasts before breaking down or failing.

FATIGUE LOAD TEST - A test in which the anchor is subjected to a specified load magnitude for 2 x 10(6) cycles in order to establish the endurance limit of the anchor.

FATIGUE RESISTANT - Opposition to breaking down or failing from use.

FATIGUE STRENGTH - The stress to which a metal can be subjected for a specified number of cyclic changes of stress.

FATIGUE STRENGTH - (Also known as Endurance Limit) Stress condition under which a material will have a life of a given number of cycles.

FATIGUE TEST - Highly polished samples are subject to stress while bending, which results in a reversal of stress for every complete revolution. The stress is reduced on each succeeding sample until the maximum stress a sample will sustain for ten million reversals has been reached. Since experience justifies the assumption that if steel can withstand ten million reversals, it can withstand such stress indefinitely. This stress is reported at the fatigue limit.

FAYING SURFACES - Two surfaces which lie close together or are in contact as a joint.

FDC OR F.D.C. - An abbreviation for (Front Dead Center). This is when the heading slide is at the end of the forming stroke and the forming operations are complete.

FEATHER (FIN) - The thin projection formed on a forging by trimming or when the metal under pressure is forced into hairline cracks or die interfaces.

FEATURE-TO-FEATURE - The linear geometrical dimensions between two specific features on a formed part or component.

FEED - The movement of a controlled length of wire into the machine for cutoff.

FEED GRIP - A tooling component in the wire line of a machine equipped with a linear feed mechanism. They are typically adjustable to cover a range of wire diameters.

FEED RATE - Refers to the speed at which a cutter can advance against a workpiece.

FEED ROLLS - A tooling component in the wire line of a machine equipped with a rotating wheel feed mechanism. They are grooved for a specific wire diameter and must be changed when the incoming wire diameter changes.

FEED TUBE - A tooling component in the wire line of a machine between the feed rolls or grips and the quill. It guides the wire through the machine and into the quill.

FEED UNITS - An accessory used for delivering the workpiece to the press or removing it from the press.

FEELER GAGE - Gage used on Direct Tension Indicating flatwashers to determine when the proper bolt tension is achieved.

FEMALE THREAD - Another name for internal threads.

FEP(R) (PLASTICS) - Fluorinated ethylene propylene has a low friction coefficient, is resistant to weathering and is useful from cryogenic temperatures to about 390F. It has a low dielectric constant and is flame and ignition resistant. Although its mechanical properties are not equal to some other engineering fluroplastics, it is commonly used for eletrical insulation, cable sheating, and as chemically resistant coatings and films.

FERRALIUM - Is a type of Super Duplex Stainless Steel which is optimized for use within fasteners.

FERRIT BY POINTE COUNT (ASTM E562) - This test method is based upon the stereological principle that a grid with a number of regularly arrayed points, when systematically placed over an image of a two-dimensional section through the microstructure,can provide.

FERRITE - Pure iron that has very low solubility of carbon.

FERRITE BY POINTE COUNT (ASTM E562) - This test method is based upon the stereological principle that a grid with a number of regularly arrayed points, when systematically placed over an image of a two-dimensional section through the microstructure, can provide, after a representative number of placements on different fields, an unbiased statistical estimation of the volume fraction of an indentiflable constituent or phase.

FERRITIC - Ferritic stainless steels contain no nickel but have a high chromium content providing greater corrosion resistance than martensitic stainless but much less than austenitic stainless. 400 series stainless usually makes up this group.

FERRITIC NITROCARBURIZING - A surface treatment process of ferrous metals involving diffusion of nitrogen and carbon into workpiece during ferritic phase, as opposed to austentic phase, for purpose of increased fatigue limit.

FERRITIC NITROCARBURIZING - A surface treatment process of ferrous metals involving diffusion of nitrogen and carbon into workpiece during ferritic phase, as opposed to austentic phase, for purpose of increased fatigue limit.

FERROUS METALS - Anything made of or containing iron. Ferrous metals include carbon and alloy steel as well as stainless steel. Metals are magnetic and are vulnerable to rust and corrosion.

FIBER - A characteristic of wrought metal, including forgings, indicated by a fibrous or woody structure of a polished and etched section, and indicating directional properties. Fiber is chiefly due to the extension of the constituents of the metal synonymous with flow lines and grain flow in the direction of working.

FIBREGLASS - Is used in studs and nuts for applications when the fastener should be non-corrosive, low in conductivity, or transparent to electromagnetic waves.

FIELD HEADING - When cold forming a solid rivet in installation with a hammering tool

FILL - A term used to indicate the extent that the metal fills the die impression or to express the success in accomplishing a desired shape by under or over filling an impression

FILLER - A tooling component that fills up the space behind pins and inserts

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 - The concave junction at two intersecting surfaces of a fastener. Often used to describe the junction between the head and shank of a threaded fastener.

FILLET - The concave intersection of two surfaces. In forging, the desired radius at the concave intersection of two surfaces is usually specified.

FILLET - A radius between two meeting surfaces.

FILLET RADIUS - The concave junction at two intersecting surfaces of a fastener.

FILLISTER HEAD - Rounded top surface, like a pan head, cylindrical sides, and a flat bearing surface. Smaller diameter head than a round head and with a correspondingly deeper slot. Fillister heads can be shaved & drilled. The smaller diameter head increases the pressure applied on the smaller area and can be assembled close to flanges and raised surfaces. Headed in counter bored dies to insure concentricity, they may be used successfully in counter bored holes. Also used heavily in electrical applications. See Cheesehead Screws, where the head height is approximately half of its diameter and typically features a slot drive. The head is also flat on top.

FIN - A form of key under the head of a fastener which serves to keep the fastener from turning during assembly and use.

FIN - The thin projection formed on a forging by trimming or when metal is forced under pressure into hairline cracks or die interfaces.

FIN NECK - A style of neck consisting of two or more fins under and integral with the head. Example: Fin Neck Carriage Bolt.

FINDER SLEEVE - A sleeve used on slotted bits that slides over the slotted fastener preventing the bit from slipping out of the screwing while driving it.

FINE BLANKING - A specialized type of blanking that fully penetrates the metal before the blank is released. This form of blanking produces no fracture zone and significiantly reduces burrs and other imperfections.

FINE BLANKING - Also known as fine-edge blanking, fine blanking is a highly accurate process of creating blanks that have smooth edges. After blanking operations have been performed on the piece of sheet metal, the created blanks are ejected from the machine for further processing.

FINE GRAIN - The result of Aluminum Killing

FINE THREAD - A type of thread with a smaller pitch and a greater number of threads per inch than the same diameter of a coarse thread. Can support greater tensile loads due to the increase in tensile stress area. Fine threads allow for grater adjustment accuracy and are less likely to loosen than coarse threads.

FINGER - A replaceable tooling component usually attached to the transfer arms and used to grip the formed part. Typically made from low carbon steel with a wear resistant layer of the gripping surfaces.

FINGER PATH - The graphical representation of the opening movement of the transfer fingers in relationship to the heading slide motion or the closing movement of the transfer fingers in relationship to the die kickout motion.

FINGER SPREADING UNIT - A special transfer unit for the CNF transfer with limited finger opening capability. Fingers were opened with a probe mounted on the tool holder.

FINISH - (1) The forging operation in which the part is forged into its final shape in the finish die. If only one finish operation is scheduled to be performed in the finish die, this operation will be identified simply as finish; first, second, or third finish designations are so termed when one or more finish operations are to be performed in the same finish die. (2) The surface condition of a forging after machining. (3) The material machined off the surface of a forging to produce the finish machine component.

FINISH (NAIL) - A wire nail that that has a head only slightly larger than the shank; can be easily concealed by countersinking the nail slightly below the finished surface with a nail-set and filling the resulting void with a filler such as putty, spackle or caulk; often used for light fastening of interior trim work, finish carpentry and cabinetry.

FINISH ALL OVER (F.A.O.) - Designation that a forging must have sufficient size over the dimensions given on the drawing so that all surfaces may be machined in order to obtain the dimensions shown on the drawing. The amount of additional stock necessary for the machining allowance depends on the size and shape of the part, and is agreed on the vendor and the user.

FINISH ALLOWANCE - The amount of stock left on the surface of the forging to be removed by subsequent machining. Also called Machining Allowance or Forging Envelope.

FINISH PUNCH HOLDER - The tool holder for the second blow on a machine with a punch rocker.

FINISH TRIM - Flash removal from a forging; usually performed by trimming, but sometimes by band sawing or similar techniques.

FINISHED FASTENER - A fastener made to close tolerances and having surfaces other than the threads and bearing surface finished to provide a general high-grade appearance.

FINISHER (FINISH IMPRESSION) - The die impression that imparts the final shape to a forged part.

FINISHING DIES - The die set used in the last forging step.

FINISHING TEMPERATURE - The temperature at which hot mechanical working of a metal is completed or discontinued.

FIRST GRIP - For a given type and thread size, the part with the lowest value of grip range is commonly referred to as a first grip part.

FIT - 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.

FITTING FACTOR - A supplemental factor of safety used in analysis of bolted joints to account for uncertainties in load paths and stresses.

FIXTURE - Tooling designed to locate and hold components in position.

FL - Length of a compression spring

FLAKES - Randomly oriented internal thermal cracks (shatter cracks) in steels resulting from critical combinations of stress and hydrogen content. In a fracture surface, flakes appear as bright silvery areas; on an etched surface they appear as short discontinuous cracks.

FLAME HARDENING - A process for hardening the surfaces of harden able ferrous alloys in which an intense flame is used to heat the surface layers above the upper transformation temperature, whereupon the workpiece is immediately quenched.

FLAME HARDENING - A process for hardening the surfaces of hardenable ferrous alloys in which an intense flame is used to head the surface layers above the upper transformation temperature, whereupon the workpiece is immediately quenched.

FLAME STRAIGHTENING - The correction of distortion in metal structures by localized heating with a gas flame.

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 lock bolt.

FLANGE - Formed projection or rim of a part generally used for stiffness or assembly.

FLANGE - A projecting rim or edge of a part; usually narrow and of approximately constant width for stiffening or fastening. See Rib.

FLANGE - Projecting rim.

FLANGE (NUTSERT) - The disc-shaped rim formed on the end of a cylindrical object, often related to the head geometry of a fastener.

FLANGED COLLAR - A type of lockbolt collar with a flange, which provides an increased bearing surface.

FLANGING - Flanging uses dies, presses, or specialized machinery to introduce a flange onto a component. It should not mark or wrinkle the material.

FLANK - The straight sides of the thread profile that connects the root to the crest.

FLANK ANGLE - The angle between the flank and a perpendicular line that intersects the root. Half the angle of a thread (30 degrees) when the threads are symmetrical.

FLANK ANGLE - The angle formed by a thread flank and a line perpendicular to the axis. For machine screw threads the flank angle is 30 degrees.

FLARING FASTENER - A fastener having a thin wall shank or barrel which is formed outward during installation to hold it in place from the opposite side of the panel.

FLASH - 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 - Metal in excess of that required to fill completely the blocking or finishing forging impression of a set of dies. Flash extends out from the body of the forging as a thin plate at the line where the dies meet and is subsequently removed by trimming. Because it cools fastener than the body of the component during forging, flash can serve to restrict metal flow at the line where dies meet, thus ensuring complete filling of the impression. Also see Closed-Die Forging.

FLASH - The excess metal forced out between the edges of the forming dies.

FLASH - In heading work the material between the die and the finish punch is referred to as the flash.

FLASH EXTENSION - Portion of flash remaining after trimming. Flash extension is measured from the intersection of the draft and flash at the body of the forging to the trimmed edge of the stock.

FLASH LAND - Configuration in the blocking or finishing impression of forging dies designed to restrict or to encourage the growth of flash at the parting line, whichever may be required in a particular case to ensure complete filling of the impression.

FLASH LAND - The line left on a forging after the flash has been trimmed off. See Parting Line.

FLASH PLATING - A very thin deposit of metal, sufficient to give a solid color.

FLASH, INTERNAL - That portion of the flash located entirely within a forging or enclosed by two or more forgings within a cluster of forgings.

FLASHLESS FORGING - TRUE closed die forging in which metal deformed in a die cavity permits virtually no excess metal to escape.

FLAT DIE FORGING (OPEN DIE FORGING) - Forging worked between flat or simple contour dies by repeated strokes and manipulation of the workpiece. Also known as Hand or Smith forging. See Open-Die Forging

FLAT HEAD - Flat top surface and a conical bearing surface with a head angle of approximated in applications where protrusion of the fastener above the mating surface is unacceptable . Use a protrusion gage when measuring head height.

FLAT HEAD - A style of blind threaded insert having a head with a rectangular cross section. Flat head inserts typically have relatively thick heads and therefore provide high levels of push-out strength. For this style of part head projects above the panel after installation.

FLAT HEAD - TRIMMED - A flat head with a smaller diameter and lower head height than a standard flat head. See Undercut Flat Head.

FLAT HEAD METRIC 90 - A countersunk head with a flat top surface and a cone-shaped bearing surface with a head angle of approximately 90 degrees. Used in applications where protrusion of the fastener above the mating surface is unacceptable. Use a protrusion gage when measuring head height.

FLAT HEAD UNDERCUT - Similar to an 82 degree flat head except that the head is undercut to 70% of its normal side height. Standard for short lengths because it allows greater length of threads. Also avoids transition fillet and assembly interference.

FLAT LOAD - How much load (force) will be required to elastically deflect the Belleville spring completely. Load is measured by force in lbs., for Imperial and in Newtons for metric sizes.

FLAT OR MATTE - Coating surface which displays no gloss when observed at any angle; a perfectly diffused reflecting the surface.

FLATTED SHAFTING - About 6% more torsional holding power can be expected when a screw seats on a flat surface. Flatting, however, does little to prevent the 0.01-in. relative movement usually considered as a criterion of failure. Axial holding power is the same.

FLATTENER - Usually a flat surface cut to an exact depth below the parting line in each die to widen the material so as to more nearly cover the next impression.

FLATTENING - The forging operation of flattening the forging stock prior to further working.

FLEXIBLE MFG. SYSTEMS (FMS) - An integrated manufacturing capability to produce small numbers of a great variety of items at low unit cost. FMS is also characterised by low change over time and rapid response times.

FLEXURAL MODULUS - A mechanical property that describes a material's resistance to bending

FLOAT - A unique capability in some multi piece fastener assemblies which allows movement of a component within a fixed housing. The capability is useful in misaligned structures, or to ease tolerance controls in the location of mating holes. Example Floating Plate Nuts

FLOATING - The ability of a fastener to move in a direction parallel to the mounting panel and allow for mating hole misalignment.

FLOATING DIE - (1) A die mounted in a die holder or a punch mounted in its holder such that a slight amount of motion compensates for tolerance in the die parts, the work, or the press. (2) A die mounted on heavy springs to allow vertical motion in some trimming, shearing, and forming operations.

FLOATING PUNCH - A tooling design where the punch is supported in the case of O-rings. This design allows the punch to move slightly to accommodate any mis-alignment between the punch and die.

FLOATING TYPE FLANGE JOINT - A conventional flanged joint in which a gasket is compressed by bolts - the gasket is not rigidly located. Calculation methods such as the ASME code in the USA and the EN1591 code in Europe.

FLOCCULATE - To aggregate into larger agglomerates to increase in size to the point where precipitation occurs, or to facilitate precipitation.

FLOW LINES - Patterns in a forging resulting from the elongation of nonhomogeneous constituents and the grain structure of the material in the direction of working during forging; usually revealed by macro-etching. See Grain Flow

FLOW STRESS - A measure of materials resistance to deformation and depends upon such things as temperature and strain rate.

FLOW STRESS - A fundamental property that describes a material's resistance to being deformed or having its shape changed. A material with a higher flow stress will be more difficult to form and require more load to deform it.

FLOW-THROUGH - A forging defect caused by metal flow past the base of a rib with consequent rupture of the grain structure.

FLUORESCENT MAGNETIC PARTICLE INSPECTION - Inspection with either dry magnetic particles or those in a liquid suspension, the particles being coated with a fluorescent substance to increase the visibility of the indications.

FLUORO-CARBON THREAD COATING - A low friction coating applied to threads. This type of coating is frequently used to prevent thread fouling when an assembly containing threaded fasteners is painted. Unless masked in some way before painting, electro deposited primers can cover the threads. If this occurs assembly difficulties can result unless the expensive chore of cleaning the threads is completed. A fluoro-carbon thread coating eliminates the need for masking or cleaning since paint will not adhere to the coating. This type of coating can also prevent problems caused by weld splatter obstructing the threads of weld nuts during their placement. Such coatings also have the property of reducing the torque-tension scatter during tightening.

FLUSH - The ability of a fastener to be contained completely within the thickness of a panel.

FLUSH - The ability of a fastener to be contained completely within the thickness of a panel. Also refers to the absence of a protrusion above the surface of the panel.

FLYWHEEL - A component that constantly rotates when the press motor is energized. The flywheel stores and releases energy during the nonworking and working portions of the press cycle respectively. The rotational energy of inertia helps prevent excessive or sudden changes in speed.

FLYWHEEL BRAKE - A mechanism used to stop the motion of a flywheel. It is a safety device that is typically engaged before entering the die area.

FMEA - A design review process referring to failure mode effect analysis.

FMECA - A design review process referring to failure mode effect criticality analysis.

FOD OR F.O.D. - An abbreviation for Face of Dies. This is the front face of the dies.

FOLD - A forging defect caused by folding the metal back on its own surface during its flow in the die cavity. See Lap.

FOLD - A flaw on a part where a gap has been closed without fusion.

FOLLOWING FLANK - The flank of a thread opposite to the leading flank.

FORCE MULTIPLIER - A dimensionless factor that is used to describe the relative force requirement of a forging or a forging section.

FORGEABILITY - The relative ability of material to deform without fracturing, rupturing, or developing flaws. Also describes the resistance to flow from deformation.

FORGING - The process of forming a product by hammering or pressing. When the material is forged below the recrystallization temperature it is said to be cold forged. When worked above the recrystallization temperature it is said to be hot forged.

FORGING - The process of working metal to a desired shape by impact or pressure in hammers, forging machines (upsetters), presses, rolls, and related forming equipment.

FORGING BILLET - A wrought metal slug used as forging stock.

FORGING CRACKS - This may occur during fastener manufacturing at the cutting or forging operations and are located on the top of the head or on the raised periphery of indented head bolts.

FORGING DIES - Forms for making forgings; they generally consist of a top and bottom die. The simplest will form a completed forging in a single impression; the most complex, consisting of several die inserts, may have a number of impressions for the progressive working of complicated shapes. Forging dies are usually in pairs, with part of the impression in one of the blocks and the rest of the impression in the other block.

FORGING MACHINE (UPSETTER OR HEADER)) - A type of forging equipment, related to the mechanical press, in which the main forming energy is applied horizontally to the workpiece, which is gripped and held by prior action of the grip dies.

FORGING PLANE - The plane that includes the principal die face and is perpendicular to the direction of ram travel. When parting surfaces of the dies are flat, the forging plane coincides with the parting line.

FORGING QUALITY - Term describing stock of sufficiently superior quality to make it suitable for commercially satisfactory forgings.

FORGING REDUCTION - Ratio of the cross-section areas before and after forging; sometimes refers to percentage reduction in thickness.

FORGING ROLL - Also known as reducer roll. A machine situated alongside the forging machine for pre-forming. The operation is carried out be passing the work-piece between contra-rotating shafts, which carry appropriately shaped dies.

FORGING STOCK - A wrought rod, bar, or other section suitable for subsequent change in cross section by forging.

FORGING STRESSES - Elastic residual stresses induced by forging or by coding from the forging temperature. They can be relieved by subsequent annealing or normalizing.

FORM OF THREAD - The profile of a thread in an axial plane for a length of one pitch.

FORM ROLLING - Hot rolling to produce bars having contoured cross sections; not to be confused with the roll forming of sheet metal or with roll forging.

FORMABILITY - The relative ease with which a metal can be shaped through plastic deformation.

FORMAPAK - The quick change die set assembly for FORMAX & FORMAX Plus machines allowing for rapid changeover from one job to the next.

FORMED TAB - Small flange bent at an angle from the body of a metal workpiece.

FORMING - Operation converting a flat sheet metal workpiece into a three dimensional part.

FORMING - Forming is a catch-all term that refers to the processes and techniques that are used to form or shape blanks.

FORWARD EXTRUSION - When metal is forced through a smaller diameter orifice thereby reducing its diameter and increasing its length. The starting material may be partially or totally contained in the tooling before the start of extrusion.

FOUR SLIDE STAMPING - A horizontal stamping process where the tools strike and form the workpiece from four orthogonal directions.

FOUR-SLIDE STAMPING - In four-slide stamping operations, four different tools are used simultaneously on the component to bend it into complex shapes. The biggest advantage of four-slide stamping is its flexibilty. The process lets technicians custom design and process intricate parts with precision.

FPY - A product yield term meaning first pass yield.

FRACTURE POINT - The point at which failure occurs and a part under stress breaks.

FRACTURE TOUGHNESS - The resistance of a given material to catastrophic failure in the presence of an existing sharp crack.

FRAME - The main structure of a press.

FREARSON - A drive recess similar to Phillips drive, but with less tapered slots.

FREARSON - The Frearson screw drive is also known as the Reed and Prince screw drive and is similar to the Phillips drive, but the Frearson has a sharp tip and larger angle in the V shape. One advantage over the Phillips drive is that one driver or bit fits all screw sizes. The tool recess is a perfect, sharp cross, allowing for higher applied torque, unlike the rounded, tapered Phillips head, which can cam-out at high torque.

FREE ANGLE (SPRING TERM) - The angular relationship between the arms of a torsion spring which is not under load.

FREE COUNTERBORE - That portion of the counterbore, remaining after the fastener is bulbed. Which is not contained within the panel when the part is properly positioned in the panel. The free counterbore is available to form the bulb.

FREE GAP - The distance between the "Free Ends" of a ring or spring as it rests in its free state.

FREE LENGTH (LO) - The length of a spring when it is not loaded.

FREE-MACHINING-STEEL FORGINGS - Those made from steel with special alloying-element additions to facilitate machining.

FRENCH RECESS - Also known as BNAE NFL22-070 by its standard number. A cross-head screw with two-step driver design, with the blade diameter stepping up at a distance from the point.

FREQUENCY (NATURAL) (SPRING TERM) - The lowest inherent rate of free vibration of a spring itself (usually in cycles per second) with ends restrained.

FRETTING - Surface damage that results when there is relative motion between solid surfaces in contact under pressure.

FRETTING CORROSION - Occurs when vibration causes a stainless fastener to continually rub against another surface, resulting in the passive film on stainless rubbing off. Fretting corrosion might occur in high tensile fasteners such as martensitic stainless.

FRICTION - Mechanical resistance to the relative movement of two surfaces. There are two main types of friction: STATIC FRICTION and DYNAMIC FRICTION. Typically static friction is greater than dynamic friction.

FRICTION DRAG - A device built into the tooling to apply resistance to the kickout pins within the tool set. The resistance applied holds the kickout pins at their end of kick positions and aids in the transferring of the part into the tooling.

FRICTION FACTOR - A factor that, when multiplied by the flow stress, expresses the friction shear stress.

FRICTION STABILIZERS - Coating materials used on fasteners with the intention of reducing the scatter in the thread and bearing surface friction coefficients.

FRICTION TYPE JOINT - A joint that employs friction (created by clamp force) between the bolt and joint members in order, to avoid shear and keep the joint members from slipping.

FRICTONAL COEFFICIENT - A unit-less value that is the ratio of the weight of an object to the force acting on the object. In bolted joints, this value deals with the friction developed between the bearing surface and clamp member or the friction between mating threads.

FRONT COUNTERSUNK - The countersink on the front or out end of the part in screw machine work.

FULL ANNEALING - The annealing of a ferrous alloy by austenitizing and then cooling slowly through the transformation range.

FULL BODY or NOMINAL DIAMETER BODY - 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'.

FULL COLLAR - A standard full-height lockbolt collar.

FULL DIAMETER BODY - ASME B18.12-2001 The unthreaded portion of a shank whose diameter is generally within the dimensional limits of the major diameter of the thread. NOTE Some fastener specifications refer to the full diameter body as the full cylindrical portion of the shank or simply as a shank.

FULL HEX - A style of blind threaded insert in which the shank has a hex shape for the entire part length. The hex shank is designed to be installed in a hex hole and offers improved spin-out resistance. The need to orient the part in the mounting hole during installation is generally considered a disadvantage.

FULL SCALE VALUE (FSV) (GAGING) - The numeric equivalent of the graduated display. FSV is usually 1-1/2 to 2 times greater than the tolerance being measured to show approach or oversize conditions.

FULL TUBULAR RIVET - A rivet with a cavity extending more than half of the length of the shank.

FULLER (FULLERING IMPRESSION) - Portion of the die that is used in hammer forging primarily to reduce the cross section and lengthen a portion of the forging stock. The fullering impression is often used in conjunction with an edger (or edging impression).

FULLERING - Reducing the cross section of a forging between ends of stock.

FUNCTIONAL - A term that is applied both to methods of gaging and to pitch diameter measurements. Functional implies the equivalent size that would be seen by a mating thread with perfect thread form. Functional gaging is accomplished by using gage members with a nearly perfect thread form. For external threads functional sizes will always be larger than single element sizes and for internal thread form functional sizes will always be smaller than single element sizes.

FUNDAMENTAL DEVIATION - An intentional clearance between internal or external thread and the design form of the thread when the thread form is on it's maximum metal condition. For metric threads the fundamental deviation are designated by letters, capitals for internal threads and small letters for external threads. Some tolerance classes have a fundamental deviation of zero. For imperial threads the fundamental deviation is called the allowance.

FUNDAMENTAL TRIANGLE HEIGHT - The fundamental triangle height is normally designated with the letter H. This is the height of the thread when the profile is extended to a sharp vee form. For 60 degree thread forms such as metric and Unified thread series, H equals 0.866025 times the thread pitch.