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Allowance – The prescribed difference between the design thread form and basic size.  Allowances can be used either to accommodate thread coatings or facilitate assembly.

Anneal – The process of reducing the hardness and increasing the ductility of metal parts by heat treatment.  Steel, stainless steel and brass blind threaded inserts are typically annealed to reduce the upset or installation load required and to reduce the risk of fracture at the outer perimeter of the bulb.

Anvil/Pemserter – The portion of installation tooling which does not move during the stroke of the installation press.  Also see Installation Punch.

Axis/Axis of Thread – Axis of the pitch cylinder.


Back Countersink – In screw machine work it is the countersink on the back or cutoff end of the part.

Back Face – In screw machine work, to face the back or cutoff end of a part after it has been cutoff while the work piece is held in the pickoff collet.

Back Work – General term applied to any operation done in the screw machine after the part has been cut off and is being held in the pick-off collet.

Barrel – Long cylindrical portion of a fastener.  Most commonly used in reference to a cylindrical portion of a standoff.  Also applied to the cylindrical portion of type FE and PL locknuts.  Sometimes applied to the cylindrical portion of type B nuts.

Basic/ Basic Size – Theoretical size from which the limits of size are derived by applying allowances and tolerances.

Best Wire Size – The diameter of a wire that will contact the thread flank at the pitch diameter.  Best wire size can be calculated from thread pitch and flank angle using simple geometry.

Blank – 1) A stud that has been headed but has not yet been thread rolled.  2) A defective condition in which a part is supposed to contain a thread, but does not contain a thread.

Blank Diameter – Sometimes referred to as the before rolled diameter.  The diameter of the pin portion of a headed stud onto which threads will be rolled.

Blind Threaded Insert – Applies to an internal thread that does not go all the way through the product.

Blow-Out (Mounting Hole) – Panel material sheared away during a hole punch operation causing the die side of the panel to exhibit a larger diameter hole than the punch side.

Blow Out (Fastener) – A defective condition which occurs on cold formed or headed nuts at the piercing operation.  Visible indication of blow out is missing material at the piercing punch exit side.

Blow up – A term used in screw machine work to indicate a change in external dimensions which occurs in thin wall parts when they are tapped.

Body – The main portion of the fastener.  Most frequently used as a synonym for the outside diameter of the head on an S type nut.

Bottom Feed – Particular type of automatic installation tooling in which the part is automatically presented onto the anvil.

Broach – Term used to indicate the manufacture of a non-round hole.  Also sometimes used as a noun to indicate the non-round hole.  The square holes in type R retainers and the hex hoes in type PL are produced by broaching.

Broaching – The act of cutting a shape in any object by using a mandrel of a similar shape.  As applied to fasteners, the way a knurled shank “broaches” its way into the mounting hole.

Bubble – The largest diameter portion of the locking feature on type LK nuts.

Bulb – The largest diameter portion above the flange on type SSC or SSA snaptop standoffs.  Also sometimes used to mean the same as bubble on type LK nuts.

Bulb Diameter – The diameter of the bulb. When an insert is used near max grip the bulb diameter will be smaller than when the insert is used near min grip.  Thick wall parts have historically been designed to provide a bulb diameter of 125% of shank diameter at max grip and 135% of shank diameter at min grip.

Bulge – See Panel Bulge.

Burst – A seam or other wire defect which opens up when the material is upset


Captive – The ability of a fastener to remain securely attached to a panel or stay within another fastener.

Captive screw – See Panel Fastener.

Center-Line to Edge Distance – The minimum distance from the edge of a panel to the center of the mounting hole that a self-clinching fastener can be installed without causing a distortion or bulge in the panel.

Chamfer – A beveled edge or corner.

Chamfer – A angle cut (typically 45°) applied to an O.D. corner of a part to eliminate the sharp corner.

Class/Class of thread – Alphanumeric designation to indicate which one of several standard grades of tolerance and allowance are being specified.

Closed End – 1) The term used in the blind threaded insert industry to describe an internal threaded insert with metal enclosing the end of the thread opposite the head.  2) In the self-clinching fastener industry this style of part is said to be blind or have blind thread.  Closed end parts are used to prevent long screws from interfering with other components or for protecting the mating threads from corrosive environments. See blind threaded inserts.

Closing – Term applied to the operation of deforming the threads of type FE/LC/LK/UL nuts to provide prevailing thread lock.

Cold Working – See work hardening.

Cone Blow – The first blow struck in a single die 2 blow header.  It gets its name from the shape of the first punch which is typically that of a frustum of a cone.

Counterbore – That portion of the axial length of which is drilled to a larger diameter than the remaining portion of the part.

Countersink – An angular cut (typically 30° to 60°) that is applied to the intersection of a hole and an end of a part to eliminate the sharp corner which would otherwise be present.

Countersunk Head – A style of blind threaded insert with an angle, typically 100 degrees included, on the shank side of the head.  If a proper size countersink is applied to the mounting hole, this style of part will be flush in the panel on the head side after installation.

Cold Flow – The movement of a ductile material under pressure.

Concealed-Head – A type of fastener which, when installed, is completely hidden when viewed from the reverse side. Installed into a blind hole.

Crest – That surface of the thread, which joins the flanks of the thread and is farthest from the base from which the thread projects.  For external threads the crest is a t the major diameter.  For internal threads the crest is at the minor diameter.

Crimp Locking Feature – A squeezed portion of an internally threaded fastener that is used to prevent a mating screw from backing out due to vibration.


Die Side Installation – The installation of a fastener into the die side of a punched mounting hole in a panel.  The die side of a hole usually exhibits blow out and is larger in size than the punch side of the hole.

Dimple – The cone shaped indentation which is applied to the point end of type FH and HFH studs and to the head end of type TFH studs.  The dimple is a registered trademark and is used to tell PEM® studs from studs manufactured by competitors.

Dimpling – Term used to describe the act of applying the thread lock to SI inserts.

Displacer – The portion of a self-clinching fastener that moves, or displaces, the panel material.  Usually the head, lugs, or knurled portion of the fastener.  It could be a cylinder, a knurl, or a hex.

Double Knurling – A defective condition which occurs when a knurl does not track properly and produces twice as many teeth per inch on the work as were present on the knurling wheel.

Drunkenness – An old term which has now been replaced by the politically correct term helix variation.

Ductile – Material property, usually describing metal, which is not brittle and can be easily formed or bent.  Clinching works in ductile material only.


Expanding Fastener – See Self Expanding / Crush Clinch.

External/External Thread – Is a screw thread form applied to the outside wall of a cylinder.

Extrusion – Creating a shape by forcing metal through a die.  Extrusion produces long, continuous shapes that may not vary in cross section over the length.  Typically extrusions are cut to shorter lengths.  Aluminum is readily extruded, but other alloys can be as well (think PlayDoh™ factory!).  A product example is the RAA.


Face – In screw machine work the operation of removing material from the out end of the part.

Face Step – In type FH studs the cylindrical step between the ribs which is used to control the roundness of the head.

Failure Mode – A description of the manner in which the failure occurred.

Fastener Hardness – The measure to approximate the strength of a fastener.  Usually measured in the Rockwell or Rockwell Superficial Scales.

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.

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°.

Flare-Mount – See Flaring Fastener.

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

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 the head projects above the panel after installation.

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

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.  See Sub Flush.

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.

Front Countersink – The countersink on the front or out end of the part in screw machine work.

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.  See Half Hex.

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.  See also Single Element.


Galling –Often referred to as “cold welding”, galling most often occurs with stainless steel fasteners when excessive heat generated by thread friction causes localized welding of small high spots on the mating thread surfaces.  Continued rotation tears chunks of material from one of the thread surfaces generating a rough, pocked surface condition.  When rotation stops some of these welds remain intact, making the threads difficult to disassemble.

Grip – The actual thickness of the panel or stack up of panel into which the insert is installed.  All performance testing of blind threaded inserts should report the grip used, as it can have a significant effect on performance

Grip Range – Range of panel thickness values into which a given part can be properly installed.  It is common practice in the blind threaded insert industry to embed the maximum grip into the end of the part.

Groove – A channel in the surface of a part which can be used to retain material, lock mating parts in place, or as a part identifier.  Also see Undercut.

Groove – That portion of the thread form that does not contain material.  See also Ridge.


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 spin-out resistance.  The need to orient the part in the mounting hole during installation is generally considered a disadvantage.

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.

Head – 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 Chamfer – The chamfer at the O.D. of the head.  Primarily applied to type S and similar style nuts.

Head Countersink – The countersink on the head end of the part.

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.

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


Injection Molding – Creating a shape by injecting a material into a cavity where the injected material fully fills the cavity under pressure.  When pressure is relieved, the part is ejected from the cavity.  The final part will retain the shape of the cavity.  Typically materials are plastic, but Metal (called MIM, or Metal Injection Molding) is also possible.  A product example is the PSSR (Snap-In Panel Fastener Retainer).

Installation Force – A term expressed in Pounds, Tons, or Newtons applied axially top a self-clinching fastener to achieve proper installation.

Installation Load –  The force required to completely form the bulb during installation.  Thick wall parts have higher installation loads than thin wall parts.  The installation mandrel must transmit the installation load and therefore blind threaded fasteners are typically not offered in sizes smaller than #4-40 or M3.  Also known as upset load.

Interference Fit – The insertion of one member into another whose diameter is slightly smaller that the part being inserted.

Internal/Internal Thread – A screw thread form applied to the inside of a hole.


Jack-Out – A testing method that applies torque to a fastener to pull it out of a panel.


Kapton™ Patch – High temperature resistant adhesive piece applied to the top of the product to allow for vacuum pick and place.

Key – A single lug of metal applied at the intersection of the head and shank.  It engages a mating notch in the panel to provide increased spin-out resistance.  The required notch in the panel is often difficult to produce and the insert must be carefully aligned during installation.

Keyed – A style of blind threaded insert that uses a key for increased spin-out resistance.

Knurl – A tooth pattern applied to a part to give it resistance to rotation.

Knurled Clinching Ring – The displacer portion of a fastener, which has corrugations and is used to develop torque resistance when installed in sheet metal.

Knurl Platform – In screw machine work the step which is present on the part before the knurling operation.


Lead – 1)Axial movement of a threaded part rotated one turn in its mating thread.  2)The axial distance from one point of the thread to the corresponding point on the next thread which is on the same helix as the first thread.

Lead Angle – The angle between the helix of the thread at the pitch line and a plane perpendicular to the axis of the thread.

Lead Free – Solder that contains no lead (meets up and coming industry standards).

Length of Engagement – The axial distance over which the two mating threads are engaged.

Lugs – The anti-rotation feature applied to studs.  Also referred to as ribs.


Major Diameter – The diameter of an imaginary cylinder which bounds the crest of an external thread or the root of an internal thread.

Mandrel – The threaded member of the installation tool that engages the threads of the insert and applies the installation load.  Spin-spin tools typically use a standard socket head cap screw as a mandrel.  Most spin-pull tools use a more complex mandrel, but some newer tools use a standard socket head cap screw.  To install an insert with external threads, the mandrel has internal threads.

Maximum Material Condition – A size condition in which the product contains the maximum amount of material permitted by the specified tolerance.  For an internal thread the maximum material condition occurs when all diameters are at the minimum values.  For external thread the maximum material condition occurs when all diameters are at their maximum values and root radius is at its minimum value.

Max Grip – Maximum panel thickness into which a given blind threaded insert can be properly installed.  If the panel is thicker than this value there will not be enough free counterbore to form an adequate bulb. It is common practice in the blind threaded insert industry to embed the maximum grip into the end of the part.

Maximum Nut Tightening Torque – The maximum amount of torque that can be applied to a nut without causing a failure.

Maximum screw Tightening Torque – The maximum amount of torque that can be applied to a screw without causing a failure.

MaxTite® – A trademarked name for thick wall product.  The name is intended to highlight the higher level of performance that thick wall product provides.  The trademark is used by Atlas Engineering, a PennEngineering company.

MIM – See Injection Molding.

Minimum distance – The minimum distance from the center of a fastener mounting hole to the nearest edge of a panel, which will keep the edge from deforming.  Suitable fixturing or increasing thickness of panel material may reduce this distance.

Min Grip – Minimum panel thickness into which a given blind threaded insert can be properly installed.  If the panel is thinner than this value there will too much free counterbore and the bulb will form in an uncontrolled manor.

Minimum Material Condition – A condition in which the product contains the minimum amount of material allowed by the specified tolerance.  For an internal thread the minimum material condition occurs when all diameters are at their maximum.  For an external thread the minimum material condition occurs when all diameters are at their minimum and the root radius is at a maximum.

Minimum sheet thickness – The thinnest section of a panel, usually measured in thousandths of an inch or millimeters, into which a fastener may properly be installed.  The same fastener may be installed in panels having any thickness greater than minimum.

Minor Diameter – The diameter of an imaginary cylinder which bounds the crest of an internal thread or the root of an external thread.

Mounting Hole – A properly sized, usually round, opening in a panel to accept a fastener.

Mounting Hole – The hole in a panel material which the user of a self-clinching fastener supplies in order to install the self-clinching fastener.  Mounting hole diameter is very critical and must be specific to the fastener that will be installed.

Multiple Lead Thread – Also known as multi-start thread.  A thread in which there is more than one helix.  For multiple lead threads the helix is always equally spaced, that is a double lead thread has the two helixes 180° apart where as a triple lead thread has them 120° apart.  Multiple lead threads have a steeper helix than single lead threads of the same size and pitch combination.


Nibs – The raised projections on the underside of the head of weld nuts.  During welding into the sheet the nibs melt and fuse to the sheet material.

Non-Stocked Standard Fastener – A common type of fastener marketed in a company catalog that is made to order not stocked.

Nosepiece – The structural member of the installation tool that supports the head of the fastener during installation.  With the head being supported and an axial load applied to the threads, the counterbore is placed in compression causing it to yield and create the bulb.  For spin-spin tools the nosepiece has radial serrations to prevent the insert from rotating relative to the tool.  Spin-pull tools have smooth nosepieces.  The nosepiece is sometimes referred to as an anvil.

Nut Shear Area – The cross sectional area of the nut which would need to shear in order for a nut stripping failure to occur.

Nutsert® – The original trade name used by Aerpat A. G. of Sweden to describe what is now commonly known as “T” series parts.  This style employs a different technology than other blind threaded inserts.  A fracture point is designed into the insert causing the part to break into two separate parts when the installation load is applied.  The exterior of the threaded portion has a taper which is forced into the counterbore causing it to expand radially against the wall of the mounting hole.


Out End – In screw machine work the end which is made out or opposite the cutoff end.

Overlay – A transparent large scale (generally 31.25 X) drawing of min. and max. material condition used for rapid inspection of parts.

Over Molding – This process forms a shape on top of another object.  Typically plastic is over molded onto metal or another plastic.  This process is similar to injection molding except that the cavity includes a fixture part that the injected material forms around.


Panel – The material into which a self-clinching fastener is installed.  The fastener material must be harder than the panel material for the self-clinching technology to work.

Panel Bulge – An expansion of the outer edge of a panel that had previously been straight.

Panel Fastener – A threaded screw, which is held captive to a panel and which, when disengaged from its main nut, remains fixed to that panel.

Panel Hardness – A material specification for self-clinching fasteners.   A hardness measurement of the material used for a self clinching fastener.  It is also refereed to as sheet hardness and typically expressed as a Rockwell B scale hardness with a maximum limit.

Passivation – Describes the treating of a metal with a mild oxidant (such as nitric acid) to remove iron or iron compounds by dissolution. This action forms a protective passive film on the surface of the metal. The trace iron left behind from machining and fabrication can provide sites for corrosion if left untreated.

PCB – Laminant fiberglass flat sheet.

Percentage of Thread – Ration (in %) of the actual thread height to a value of .75H.  .75H is the old value of theoretical thread height in the American National Thread Profile.  Since the design thread height of the Unified National Thread Profile is only .625H it is impossible to have a 100% thread.  In fact, maximum thread percentage would be .625 over .75 or 83%.

Pilot – For broaching fasteners such as type KF2 and KFE the cylindrical portion between the knurl and the end of the shank.  This is used to pilot the knurl into the mounting hole.

Pin – A captive post that extends from a panel.

Pin Diameter – This term is sometimes used to mean the same as blank diameter.  See definition of Blank Diameter.

Pitch – The axial distance between a point on one thread and the corresponding point on the next thread.  For single start thread the pitch and lead are equal.  For multiple lead threads pitch is equal to lead ÷ the number of thread starts.

Pitch Cylinder – An imaginary cylinder which intersects the thread form at a diameter such that the width of the thread groove and the width of the thread ridge are equal to one another and are equal to one half the pitch.

Pitch Diameter – The diameter of the pitch cylinder.  Pitch diameter is denoted by the symbol PD or by the symbol E.

Plunger Assembly – A spring-loaded device used for latching or indexing purposes.

Plusnut® – A trademarked name for slotted shank product. Originally issued to BF Goodrich, the trademark is currently owned by Rivnut-Bollhoff.

Plus+Tite® – A trademarked name for slotted shank product. The trademark is used by Atlas Engineering, a PennEngineering company.  The name identifies with the Plusnut trademark and with the “Tite” suffix of the SpinTite and MaxTite trademarks in the Atlas Engineering product line.

P/M – See also Powder Metal.

Positive Stop – A visual indication that the proper depth of penetration of the knurled ring has occurred or when the “head” is in contact with the top surface of the panel. Synonym: shoulder.

Powder Metal – Creating a shape by placing a powdered metal into a shaped cylindrical cavity and squeezing along the top and bottom of the cylinder.  The part must be carefully removed from the cylinder at which point it is said to be in the ‘green state’.  The part then gets sintered to fuse the powder granules together.  Powdered metal parts are porous and less dense than standard metal parts.  If these will later be plated, they need to be resin impregnated to seal the pores (this is done by introducing a plastic filled filter with the part in a vacuum environment).  A product example is the RAS or TDO.

Pre-bulbed – The practice of starting the bulb during the manufacture of the insert.  This is done to reduce the installation or upset load required.  The major disadvantage of this practice is that it requires a larger mounting hole to clear the bulb.  Unless a positioning step is provided under the head, the installed insert may not be concentric to the mounting hole.

Prevailing Torque – Repeatable torque that can be applied to a locking fastener.

Protrusion Anvil – See raised ring anvil.

Pull-Out – The force required to significantly yield or fracture the insert or the panel when an axial load is applied in a pulling direction from the head side.  For thin wall parts the industry standard is to support the panel with a bushing having a hole diameter of three times the fastener shank diameter. If the panel strength is adequate, the mode of failure is shear of the bulb.

Pull-Through – The resistance of a fastener to a force applied in the same direction to which it was installed.

Punch – A movable insert, either solid or hollow, which applies an installation force to the top of the fastener.

Punch/Installation Punch – On installation tooling that member of the tooling which moves when the press cycles.

Punch Side Installation – Installation of a fastener into the punch side of a pierced (punched) mounting hole.

Punched Mounting Hole – A pierced hole requiring applied load to a punch to shear panel material through a die.

Push-Out – The resistance of a self-clinching feature to axial loading.  Push-out is conducted in the direction opposite the direction of installation of a self-clinching fastener.


Raised Ring Anvil – An anvil with a protruding lip used to cold flow panel material into a self-clinching fastener from the opposite side it is installed.

Reel – Circular case in which tape is wound.

ReelFast® – PennEngineering Trademark.

Reflow Oven – Oven that melts the solder and adheres the product to the PCB and allows for set temperatures within different zones.

Ribs – Sometimes used to mean the same as lugs.  (See definition of Lugs).

Ribbed Shank – A style of insert with a knurl on the shank OD.  The knurls are typically aligned  with the long axis of the part and begin just enter the head and extend toward the thread.  Knurl length is typically equal to counterbore length.

Ridge – That portion of the thread form that contains material.  See also Groove.
Ripples – A condition that may occur on a floater assembly where as the top of the roll-over on the retainer has a scalloped or wavy appearance.

Rivet Nut: – A rivet nut, also known as a blind rivet nut or threaded insert,[1] is a one-piece internally threaded and counterbored tubular rivet that can be anchored entirely from one side. There are two types: one is designed to form a bulge on the back side of the panel as a screw is tightened in its threads. The other is similarly drawn in using a screw, but is drawn into the sleeve instead of creating a bulge.

Rivnut® – A trademarked name applied to the first blind threaded inserts developed by BF Goodrich to attach rubber flaps to airplane wings.  Originally registered in 1975, the trademark is currently owned by Rivnut-Bollhoff.  The fastener business was sold by BF Goodrich and became known as Rivnut Engineered Products, sometimes referred to as REP.  In 2000 Rivnut Engineered Products was purchased by Bollhoff, a 125-year-old European fastener company, and now uses the Rivnut-Bollhoff name.

Rockwell Hardness – A relative measure of hardness.  Rockwell C Scale is used for hard materials, Rockwell B for softer materials, such as sheet metal.

Roll Out – The large diameter created by driving an undercut blade into the step of a stud during the thread rolling operation.

Roll Over – Term applied to the portion of a type R retainer opposite the shank end.  Gets its name from the fact that during assembly this portion of the part is rolled over to captivate the insert.

Root – 1) The smallest diameter created by driving an undercut blade into the step of a stud during the thread roll operation.  2) That surface of the thread that joins the flanks of adjacent thread forms and is immediately adjacent to the base from which the thread projects.  For external thread the root is at the minor diameter.  For internal thread the root is at the major diameter.


Screw Shear Area – Cross sectional area of the screw that would need to shear in order for a screw stripping failure to result.

Sealed Head – A term used to describe any style of insert that has had a ring of elastomer applied at the intersection of the head and shank.  A typical application of a sealed head part is to fastener a roof rack to an automobile without creating a leak point.

Seam – A longitudinal surface defect in a wire product.

Second Grip – For a given type and thread size, the part with the second lowest value of grip range is commonly referred to as a second grip part.  The next grip range is a third grip part and so on.  For some thread sizes of thick wall parts, the catalog lists six grip ranges, in which case the highest grip range part would be referred to as a sixth grip part.

Self-Expanding, Crush Clinch – A fastener with a shank or barrel which is compressed during installation to hold it in place and flush from the opposite side of the panel.

Self-Clinching – The method by which a fastener is securely attached to a sheet of ductile material by causing the material to cold flow under pressure into an annular recess of the fastener thereby securely locking it in place.

Self-Locking – A locking element, formed is an integral part of a fastener, which provides force to restrict the rotational movement of a threaded member.

Shank – The entire outer portion of a blind threaded insert excluding the head.  The counterbore and the threads are both contained within the shank.  Shank diameters are typically just under the minimum mounting hole diameter with a modest minus tolerance applied.

Shank Countersink – The countersink in the shank end of the part

Shank Length – The total axial length of shank plus undercut plus displacer (definition #1). After a self-clinching fastener has been properly installed in the sheet, the distance from the top of the sheet to the end of the shank is also the shank length (definition #2).

Shaving – Term used to describe the operation of knurling, cutting the undercut, and trimming the shank diameter on concealed head studs.

Shortening – The amount of decrease in overall length that occurs when a blind threaded insert is installed.  It is typically slightly less than the free counterbore length minus two times the wall thickness.  Inserts shorten more when installed in min grip than when installed near max grip, as a result, the installed height on the blind side of the panel is essentially constant, regardless of grip.

Shoulder – The surface area of a fastener, which contacts the top surface of the sheet material. See Positive Stop.

Side Load–The load applied to the fastener parallel to the clinched panel at a given distance from the panel that will cause the clinch feature to fail or yield the panel or fastener.  Thinner panel may yield, thicker panel will cause the clinch feature to fail either by push-out on the bending compression side or pull-thru on the bending tension side.  Typically, failure occurs when the bending moment resulting from the side load and distance exceeds the bending strength of the installed fastener.  Side loads at other distances can be estimated by computing the bending moment from the published load and distance and then dividing by the distance of interest.

Single Element – A term applied to gauging methods and to thread parameters (usually P.D.) Which implies that only one particular element is being considered.  Single element readings ignore the effects of other thread elements that would contribute to functional readings.  The reading over wires is a single element reading of pitch diameter only.

Slotted Shank – The generic term for a Plusnut or PlusTite insert.  Slotting the shank allows larger grip range and also produces a larger bulb diameter than could be achieved with a slotted shank.  Slotted shank parts typically have very thick walls and therefore high upset loads.  They are sometimes pre-bulbed to reduce the upset load.

SMT – Surface Mount Technology.

Solder Pad – Tinned area on PCB over which Solder paste will be stenciled.

Solder Paste – Solder and Flux slurry.

Special Fastener – A unique fastener which is not found in a published catalog and is usually a new design but can be a modified standard part.

Spin-Out – The torsional holding power of an insert relative to the panel in the absence of any clamp load.  It is typically measured by holding the panel, inserting a screw from the thread end of the part until it bottoms against the part and applying torque until failure.  For inserts with round shanks the typical failure mode is the insert spinning in the panel.  For keyed inserts or inserts with hex shanks the values will typically be higher and the mode of failure may switch to torsional failure of the insert or thread stripping due to the induced load.

Spin-Pull – A type of tool that applies the upset load by first turning a mandrel into the threads of the insert with a low torque and then apply a pulling force to the mandrel.  After the part has been upset by the pulling action, the mandrel is turned in the opposite direction to remove it.  For this reason, a more proper term for this type of tool that is sometimes used is spin-pull-spin.  Compared to spin-spin tools, these tools are more complex, heavier, more expensive and more difficult to setup.  However, a smooth nosepiece that will not mar the insert head can be used.

Spin-Spin – A type of tool that applies the upset load by turning a threaded mandrel into the threads of the insert.  The mandrel is driven by an air motor through reduction gearing.  A thrust bearing is used to reduce frictional torque resulting from the applied load.  Spin-spin tools are light weight and inexpensive and come with varying amounts of gearing.  As thread size increases additional gearing is used to increase torque output at the expense of speed. The stall torque is adjusted by air pressure.  Operation is simple, spin in to stall and then reverse the trigger and spin out.  Hence the spin-spin terminology. To prevent the insert from rotating, a serrated nosepiece must be used and therefore significant marring of the insert head occurs.

SpinTite® – A trademarked name for thin wall product.  The name is derived from the fact that thin wall product can be installed with a spin-spin tool.  The trademark is used by Atlas Engineering, a PennEngineering company.

Spinwall Technology™ – A trademark used by AVK to describe how the technology of thin wall parts differs from that of thick wall parts.  The major difference they claim is the radial expansion of the counterbore to completely fill the mounting hole before the bulb is formed.

Spokes – Solid portion of the stencil design that holds the center of the hole to the rest of the stencil pattern.

Spring-Loaded – A device having a separate movable component that is biased in one direction by a spring.

Stamping – This process takes a length of sheet metal and forms a part by cutting and folding the metal.  This typically is a very high-speed process that yields many pieces in a very short period of time.

Stencil – Screening sheet used to apply solder paste to exposed areas of a PCB.

Step – That portion of a headed stud blank to which the root and roll out will be applied.  Sometimes referred to as the thread rolling step which can be slightly misleading as threads do not get rolled on to the step.

Strain Hardening – See cold working.

Standard Fastener – A common type of fastener marketed in a company catalog.

Standoff – A tubular device, usually threaded, for spacing or stacking components.

Stroke – The amount of decrease in overall length that occurs when a blind threaded insert is installed.  Therefore, it is numerically equal to the shortening.  However, the term stroke is typically applied to spin-pull tools whereas the shortening term is applied to the insert.  Most spin pull tools have an internal stop, which limits the stroke.  To setup these tools, the stroke must be properly adjusted so that the insert will be installed properly.

Stud – A male threaded captive post that extends from a panel.

Surface Mount – Process of applying product to PCB by first stenciling solder paste then placing product on paste and finally heating entire assembly to melt the solder.  Also known as ‘reflow soldering’.

Swaging – An operation whereby a reduced diameter of a fastener is deformed to secure it to a panel. Also see self-expanding/crush clinch.  Note: the antonym of swaging is self-clinching where the panel material is caused to deform.


Tape – Plastic carrier strip containing mechanical product.

Tensile Strength – The axial strength of a stud or nut.

Tensile Stress Area – The effective cross section area through the threaded section which resists bolt fracture in tension.  There are a variety of different methods used to calculate the tensile stress area.  All of these methods use the PD and/or the minor diameter as the basis for the calculation.

Thick Wall – A style of part having a wall thickness of roughly 14 % of the counterbore diameter.  Thick wall parts have higher installation loads and typically can not be installed with spin-spin tools.  Although they have narrower grip ranges than thick wall parts, they provide a higher level of performance.

Thin Wall – A style of part having a wall thickness of roughly 8 % of the counterbore diameter.  Thin wall parts have lower installation loads allowing them to be installed with spin-spin tools.  They also have wider grip ranges than thick wall parts, but provide a lower level of performance.

Thread Class – A measure of clearance or fit between the screw and the nut taken at the pitch diameter.

Threaded Insert – A metal fastener, usually threaded, that can provide a strong attachment point to a section of material. Threaded inserts can provide strong threads to soft materials such as plastics or composites. Other type of threaded inserts can be clinched or may utilize blind threaded rivet technology to provide strong threads in thin metal sheets. The use of threaded inserts eliminates the need for tapping or otherwise creating threads directly into the base material which may not offer the strength required or in some cases may be more costly.

Thread Form – Defined as the profile of an axial section through one complete pitch.  Basic form for Unified National and M Profile threads is a 30° flank angle with a P over 8 truncation at the major diameter and a P over 4 truncation at the minor diameter.  Design forms for internal and external threads are different from each other, may be slightly different from the basic form and represent maximum material conditions.

Throughhole – A hole, threaded or unthreaded, which transverses the entire length of a part and is usable from either end.

Tolerance – The absolute amount of maximum or minimum dimensional deviation allowed that will not affect the performance of a mechanical part.  The total amount of variation permitted on the size of a dimension.  When min. and max. dimensions are given, tolerance is the difference between the two.  Internal threads are toleranced above basic dimensions and external threads are toleranced below basic dimensions.

Top Feed – A method of automatic installation in which the fastener to be installed is presented automatically to the punch.

Torque-Out – The amount of torque necessary to spin the fastener out of the sheet.  The torsional holding power of a self-clinching fastener in a sheet.  Torque-Out testing is conducted by applying pure torsion (no axial load) to the self-clinching fastener.

Torque-Thru – An indirect measure of the tensile strength of a self-clinching fastener.  The term torque-thru is most commonly applied to studs.  Torque-thru tests on studs are conducted by placing a bushing over the stud, applying a nut and tightening until failure results from the induced tensile load exceeding the tensile strength of the stud.

Trimmed-Knurl – When a knurl platform is knurled in screw machine work, the knurl rolls over or overhangs the platform.  Knurls may be trimmed flush with the platform(-0 S type nuts) trimmed to some value slightly greater than the platform height(-1 and –2 S type nuts) or may be left untrimmed (type R retainers).

Truncation – In general terms truncation is some measure of the amount that was removed from a sharp V profile.  A truncation at the major diameter of an external thread or the minor diameter of an internal thread is known as crest truncation.  The truncation at the major diameter of an internal thread or the minor diameter of an external thread is known as root truncation.  Truncation can be measured radially in which it is generally shown as a fraction of the theoretical thread height H.  It can also be measured axially in which case it is typically shown as a portion of the thread pitch P.


Ultimate Thread Strength – The force required to cause significant yielding or fracture of an  insert when the head is supported and a load is applied to the threads in a pulling direction from the head side.  It is equivalent to the insert being over-installed to failure.  The difference between ultimate thread strength and installation load is significant in that it represents the size of the force window needed for tools that install to a constant force.  Spin-spin tools install to a constant torque, but for consistent thread friction conditions, they in fact install to a constant force.

Undercut – The triangular or rectangular shaped groove applied to the shank of a self-clinching fastener located between the displacer and the shank.  The purpose of the undercut is to accept the panel material displaced by the displacer.

Underfill – Primarily used in heading and forming work to denote a condition  in which  the work material did not completely fill the die cavity.  Most common examples are on the head of type S nuts, and on the step of studs.

Unthreaded Length – That portion of the axial length of a stud, at its head end, that is unthreaded.

Upset – A term sometimes used as a verb to describe the act of creating the bulb when installing a blind threaded fastener.  It is commonly used in cold heading and in solid riveting and has been applied to inserts because forming the bulb is similar to forming a fastener head by upsetting.

In heading work the operation of significantly increasing the diameter of the work by striking it from the end.

Upset Load – An alternate term for installation load.


VIA – Small holes on the solder pad that allow for conductivity through the board

VH Factor – In self-clinching fastener design, the ratio of the volume of the displaced material to the volume of material contained within the mounting hole

Volume Ratio – In self-clinching fastener design the ratio of displace volume to undercut volume.


Wall Thickness – The thickness of metal, per side, between the shank diameter and the counterbore diameter.

Wave Solder – Process of applying product to PCB by placing product on a solder pad and running the board over a fountain of solder that wicks up along an exposed length of product on the opposing side of the PCB.  Parts using this technology would be special products with modified design.

Wedge Head – A style of insert, usually thin wall, that has a number of wedge shaped protrusions added at the intersection of the head and shank to increase spin-out from softer materials.  Can also be used to improve the electrical connection between the insert and the panel for current carrying applications.

Wobble – Defective condition in internally threaded product in which the threads are not perpendicular to the bearing surface.

Work Hardening – Deforming metal to the point at which it an increase in hardness and strength is exhibited.  Also known as Strain Hardening.


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