Threaded FastenersThreaded Fasteners

Nomenclature and DefinitionsNomenclature and Definitions

Fastener Types Fastener Types Head StyleHead Style Drive TypeDrive Type ThreadsThreads Identification Identification GradeGrade Nuts and WashersNuts and Washers Thread RepresentationThread Representation MiscellaneousMiscellaneous

Fastener TypesFastener Types BoltBolt

• Bolts are defined as headed fasteners having external threads Bolts are defined as headed fasteners having external threads that meet an exacting, uniform bolt thread specification such that meet an exacting, uniform bolt thread specification such that they can accept a non-tapered nut.that they can accept a non-tapered nut.

• Screws are defined as headed, externally-threaded fasteners Screws are defined as headed, externally-threaded fasteners that do not meet the above definition of bolts. Screws always that do not meet the above definition of bolts. Screws always cut their own internal threads when initially installed, as there cut their own internal threads when initially installed, as there is generally no tool meeting the arbitrary specification of their is generally no tool meeting the arbitrary specification of their threads to tap out the internal threads beforehand.  Also, they threads to tap out the internal threads beforehand.  Also, they are generally tapered to a sharp point.are generally tapered to a sharp point.

• Machine Screw Machine Screw Not really a screw by definitionNot really a screw by definition no chamferno chamfer <ؽ”<ؽ” < 3.0” in length< 3.0” in length

Head StyleHead Style• FlatFlat

A countersunk head with a flat top.A countersunk head with a flat top.Abbreviated FHAbbreviated FH

• OvalOvalA countersunk head with a rounded top.A countersunk head with a rounded top.Abbreviated OH or OVAbbreviated OH or OV

• PanPanA slightly rounded head with short vertical sides.A slightly rounded head with short vertical sides.Abbreviated PNAbbreviated PN

• TrussTrussAn extra wide head with a rounded top. An extra wide head with a rounded top.

• RoundRound

A domed head.A domed head.Abbreviated RHAbbreviated RH

Head Style (cont’d)Head Style (cont’d)• HexHex

A hexagonal Head.A hexagonal Head.Abbreviated HH or HXAbbreviated HH or HX

• Hex WasherHex WasherA hex head with built in washer.A hex head with built in washer.

• Slotted Hex WasherSlotted Hex WasherA hex head with built in washer and a slot. A hex head with built in washer and a slot.

• Socket Head CapSocket Head CapA small cylindrical head using a socket drive.A small cylindrical head using a socket drive.

• ButtonButtonA low profile rounded head using a socket drive.A low profile rounded head using a socket drive.

Drive TypeDrive Type Phillips Phillips

An X shaped drive.An X shaped drive.Abbreviated - PHAbbreviated - PH

SlottedSlottedA slot in the head.A slot in the head.Abbreviated - SLAbbreviated - SL

CombinationCombinationA combination of slotted and Phillips drives.A combination of slotted and Phillips drives.Abbreviated - ComboAbbreviated - Combo

Socket, Hex or AllenSocket, Hex or AllenA hexagonal hole for use with an Allen wrench.A hexagonal hole for use with an Allen wrench.

ThreadsThreads Thread Count (TPI)Thread Count (TPI)

TPI stands for Threads Per Inch. This is simply a count of the TPI stands for Threads Per Inch. This is simply a count of the number of threads per inch measured along the length of a number of threads per inch measured along the length of a fastener. In general smaller fasteners have finer threads, so the fastener. In general smaller fasteners have finer threads, so the thread count is higher. thread count is higher.

Thread PitchThread PitchMetric fasteners are specified with a thread pitch instead of a Metric fasteners are specified with a thread pitch instead of a thread count. The thread pitch is the distance between threads thread count. The thread pitch is the distance between threads expressed in millimeters (measured along the length of the expressed in millimeters (measured along the length of the fastener). For example a thread pitch of 1.5 means that the fastener). For example a thread pitch of 1.5 means that the distance between one thread and the next is 1.5mm. In general distance between one thread and the next is 1.5mm. In general smaller fasteners have finer thread so they have lower thread smaller fasteners have finer thread so they have lower thread pitch.pitch.

Lead – Distance a bolt will travel during one complete revolution. Lead – Distance a bolt will travel during one complete revolution. (Equals pitch.)(Equals pitch.)

Thread TypesThread Types Unified Thread Unified Thread

• UNC – Unified National CoarseUNC – Unified National Coarse• UNF – Unified National FineUNF – Unified National Fine

American National ThreadAmerican National Thread Sharp-V ThreadSharp-V Thread Metric ThreadMetric Thread Whitworth ThreadWhitworth Thread Square ThreadSquare Thread Acme ThreadAcme Thread Buttress ThreadButtress Thread Rolled ThreadRolled Thread Pipe Thread Pipe Thread

• NPT – National Pipe TaperNPT – National Pipe Taper• NPS – National Pipe StraightNPS – National Pipe Straight

Unified Threads (detail)Unified Threads (detail) P = Pitch = 1/Number of threads per inch (TPI)P = Pitch = 1/Number of threads per inch (TPI) H = Angular Depth = 0.866025 x PH = Angular Depth = 0.866025 x P d = Actual Depth = 0.54127 x P or 5/8 Hd = Actual Depth = 0.54127 x P or 5/8 H Hn = Basic height of Internal Thread = 0.54127 x P or 5/8 HHn = Basic height of Internal Thread = 0.54127 x P or 5/8 H Hs = Basic height of External Thread = 0.61344 x PHs = Basic height of External Thread = 0.61344 x P H/8 = Shortening of major dia. = 0.108253 x PH/8 = Shortening of major dia. = 0.108253 x P H/4 = Shortening of minor dia. = 0.216506 x PH/4 = Shortening of minor dia. = 0.216506 x P

Thread Detail cont’dThread Detail cont’d• Crest Width = 1/8 PitchCrest Width = 1/8 Pitch

• Root Width = ¼ PitchRoot Width = ¼ Pitch

• r = Radius at the Root = 0.1443 x Pr = Radius at the Root = 0.1443 x P

Internal and External ThreadsInternal and External Threads

Thread fit comparisonThread fit comparison

Thread RepresentationsThread Representations• DetailedDetailed - - Pictorial, Time Consuming to DrawPictorial, Time Consuming to Draw

• SchematicSchematic

• SimplifiedSimplified –– Preferred method, versatilePreferred method, versatile

Thread RepresentationsThread Representations

IdentificationIdentification In the United States, the convention for describing threads is to In the United States, the convention for describing threads is to

give the length of the bolt, followed by the nominal diameter and give the length of the bolt, followed by the nominal diameter and then the number of threads per inch. So, for example, one might then the number of threads per inch. So, for example, one might ask for a “2-inch quarter-twenty bolt,” which would beask for a “2-inch quarter-twenty bolt,” which would be

• 2 inches long, 2 inches long, • have a nominal diameter of a quarter of an inch, and have a nominal diameter of a quarter of an inch, and • have twenty threads to the inch.have twenty threads to the inch.

If the bolt is smaller than a quarter-inch in diameter, the gauge If the bolt is smaller than a quarter-inch in diameter, the gauge number will precede the TPI instead of the diameter. A typical number will precede the TPI instead of the diameter. A typical smaller fastener could be “a 1-inch #8-32,” “8” being a gauge smaller fastener could be “a 1-inch #8-32,” “8” being a gauge number and “32” the number of threads per inch.number and “32” the number of threads per inch.

Thread IdentificationThread Identification

Proper annotationProper annotation• ¼-20 x 2.5 UNC 2B¼-20 x 2.5 UNC 2B

Class FitClass Fit• 1-Loose1-Loose• 2-Standard2-Standard• 3-Close3-Close

Internal or externalInternal or external• A-External threadsA-External threads• B-Internal threadsB-Internal threads

Identification (cont’d.)Identification (cont’d.) Bolt lengthBolt length

• For fasteners where the head usually sits above the surface, For fasteners where the head usually sits above the surface, the measurement is from directly under the head to the end of the measurement is from directly under the head to the end of the fastener.the fastener.

• For fasteners that are designed to be countersunk, the For fasteners that are designed to be countersunk, the measurement is made from the point on the head where the measurement is made from the point on the head where the surface of the material is, to the end of the fastener.surface of the material is, to the end of the fastener.

Thread length – Thread length – • Up to 6” bolt = 2D+1/4”Up to 6” bolt = 2D+1/4”• Over 6” bolt = 2D+1/2”Over 6” bolt = 2D+1/2”• Bolts too short for the formula are threaded up to the head.Bolts too short for the formula are threaded up to the head.• Bolts can also be designated “full thread”.Bolts can also be designated “full thread”.

GradeGrade Grade 5 fasteners are 120 ksi fasteners. This means the tensile Grade 5 fasteners are 120 ksi fasteners. This means the tensile

strength is 120,000 lbs per square inch. Grade 8’s are 150 ksi strength is 120,000 lbs per square inch. Grade 8’s are 150 ksi fasteners meaning the tensile strength is 150,000 lbs per square fasteners meaning the tensile strength is 150,000 lbs per square inch. Also, the ultimate shear strength of a fastener is typically inch. Also, the ultimate shear strength of a fastener is typically about 60% of its ultimate tension strength. So given a certain about 60% of its ultimate tension strength. So given a certain diameter (cross-sectional area) and strength rating, someone can diameter (cross-sectional area) and strength rating, someone can figure out how much load that fastener can carry in both tension figure out how much load that fastener can carry in both tension and shear. and shear.

Nuts and WashersNuts and Washers HexHex

A six sided nut. A six sided nut. Also referred to as a finished hex nut.Also referred to as a finished hex nut.

Nylon Insert LockNylon Insert LockA nut with a nylon insert to prevent backing off.A nut with a nylon insert to prevent backing off.Also referred to as a NylockAlso referred to as a Nylock

JamJamA hex nut with a reduced height.A hex nut with a reduced height.

WingWingA nut with 'wings' for hand tightening.A nut with 'wings' for hand tightening.

CapCapA nut with a domed top over the end A nut with a domed top over the end of the fastener.of the fastener.

Nuts and Washers (cont’d.)Nuts and Washers (cont’d.) AcornAcorn

Acorn nuts are a high crown type of cap nut, Acorn nuts are a high crown type of cap nut, used for appearance.used for appearance.

FlangeFlangeA nut with a built in washer like flange.A nut with a built in washer like flange.

TeeTee

A nut designed to be driven into wood to create A nut designed to be driven into wood to create a threaded hole.a threaded hole.

SquareSquareA four sided nut.A four sided nut.

K-Lock or KepK-Lock or KepA nut with an attached free-spinning external A nut with an attached free-spinning external tooth lock washer.tooth lock washer.

Nuts and Washers (cont’d.)Nuts and Washers (cont’d.) FlatFlat

A flat washer used to distribute load. A flat washer used to distribute load.

Split LockSplit LockThe most common style of washer used to The most common style of washer used to prevent nuts and bolts from backing out.prevent nuts and bolts from backing out.

External Tooth LockExternal Tooth LockA washer with external 'teeth' Used to prevent A washer with external 'teeth' Used to prevent nuts and bolts from backing out. nuts and bolts from backing out.

Internal Tooth LockInternal Tooth LockA washer with internal 'teeth' Used to prevent A washer with internal 'teeth' Used to prevent nuts and bolts from backing out. nuts and bolts from backing out.

FenderFenderAn oversize flat washer used to further distribute An oversize flat washer used to further distribute load especially on soft materials.load especially on soft materials.

FinishingFinishingA washer used to obtain a 'finished' look. A washer used to obtain a 'finished' look. Usually used with oval or flat head screws.Usually used with oval or flat head screws.

MiscellaneousMiscellaneous LH / RH ThreadLH / RH Thread Set ScrewSet Screw Shoulder BoltShoulder Bolt Carriage BoltCarriage Bolt Counter sinkCounter sink Counter boreCounter bore Thru HoleThru Hole TapTap DieDie RivetRivet PinPin KeyKey Retaining RingRetaining Ring