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General | Types (Round head, flat head, ...) | Drives (phillips, torx, ...) | Nuts | Terms

The "Machinery's Handbook" categorizes fasteners as:

  • Nails, spikes, wood screws
  • Rivets
  • Bolts, Screws & Nuts
    • Machine screws
    • Cap screws
    • set screws
    • wing screws & thumb screws.
Screw/Bolt types:
  • Bolts - Goes thru a hole and is held by a nut. *
    Sometimes large screws e.g. lag screws are called bolts.
  • Screw - Screws into a tapped (threaded) hole or self-tapping or wood screws. *
  • Machine Screw - Threaded all the way or a smaller shank allowing the screw to go all the way in.
  • Cap Screw - Typically only partially threaded with the solid part the same diameter as the outside of the threads (bolts),
      or, have machine threads and require an Allen (inhex) or other drive tool that inserts into the head.
* The "Machinery's Handbook"
I could not find any official definition of Machine or Cap screw.
The list in the table below is the way they were listed in
"The Machinery's Handbook", but round and flat head were listed as both, the illustrations were similar to the ones above.

Machine Screws
flat countersunk (82° & 100°)
oval countersunk
Cap Screws
round head
flat countersunk
socket head

bolt, screw, round head, hex head, flat, head, pan head, oval head, fillster head, button head, SHCS, Socket head cap screw, torix
Note: Drive types (slotted, phillips, torx, .. see below) are only examples. Most head types come with a variety of drive types.
Different combinations of names may be used for the same type. One common list included: Socket Head Cap, Hex Head Flange Bolts, Socket Counter Sank Head, Socket Button Head Cap Screw, Socket Set Screw, Truss, Pan, CSK (Countersunk) Heads, Round Head, cheese head, mushroom head.

phillips, slotted, combinataion, socket, hex, allen, ph, sl, torx, star, drive
Bolts and Screws (grade, torque, ...)
Screwtypes at lara.com
Fastner Type Chart at BoltDepot.com
Bolts and Screws at RoltaFasteners.com

TORX PLUS is an improved version of TORX® which extends tool life even further and permits greater torque transfer compared to TORX.

Many screw drives, including Phillips, TORX, and Hexagonal, are also manufactured in tamper-resistant form. These typically have a pin protruding in the center of the screw head, necessitating a special tool for extraction.

Pozidriv® is very common in Europe. It looks a lot like a Phillips screwhead, but it includes 4 more contact points. Common sizes are Pozidriv¨ #0, #1, #2 and #3.
pozidriv Phillips screws and drivers have an intentional angle on the flanks so they will cam out of the slot before a power tool will twist off the screw head. This is (was) a creative production approach when the device was first invented, but it leaves a lot to be desired when it comes to field service of the screws.

With improvements in production tools to better control the torque of the tool the cam-out action is not necessary, and has very little purpose (except to aggravate people). The Pozidriv screws and drivers have straight sided flanks which are, not coincidentally, much more friendly for field servicing. With Pozidriv you can apply much more torque to the screw without having the driver bit jump out of the slot.

wing, hex, domed cap, acorn, tee
Nuts - Hex Nuts, Cap Nuts, Wing Nuts, T-nuts - Bolt Depot
Terms: (See also standards below)
12N - National 12 Pitch
AN - World War II era hardware standards system. Literally "Air Force/Navy"
  or "Army/Navy." A very logical numbering system now being
  bastardized by government changeover to NAS/MS series.
FT - Fine thread (same as UNF)
FH - Flat Head
HH - Hex Head
HX - Hex Head
MS - Military Standard specification
National Coarse thread pitch (same as UNC)
NF - National Fine thread pitch (same as UNF)
NEF - National Extra Fine thread pitch
NS - National Special thread pitch
OH - Oval Head
PH - Pan Head
PH - Phillips Drive
psi - Pounds per square inch.
tpi - Threads per inch
UNC - Unified National Course thread form (same as FT)
UNF - Unified National Fine thread series

ISO - International Organization for Standardization - ISO 898-1, 1999
SAE - Society of Automotive Engineers - SAE J429
ASME - American Society of Mechanical Engineers
COFS - Committee on Framing Standards of AISI
ee Glossaries at: bonaero.com, Defense Logistics Agency

Fastner Type Chart and Nuts at BoltDepot.com
US & Metric Bolt Torque by Grade
Screw Finder at BobbyDyer.com
Screw Information at search.com
Screwtypes at lara.com
Fastener Material Chart at CenturyPerformance.com
Metric Bolt Properties Grade, Strength
Proof Loads at FullerMetric.com
Strength at AtlanticFasteners.com
ASTM, SAE AND ISO grade markings and mechanical properties for steel fasteners at AmericanFastener.com
SAE Standards for Bolts
CD Stud Fasteners Specifications at SunBeltWelding
Tap Drill Sizes
Corrosion Resistant Bolts at contractors-sources.com
Aircraft Hardware
Automotive Racing Products (ARP)- Bolts
Stainles Steel fasteners with specs for Aluminum, Titanium also at ssina.com
Fastener and Screw / Bolt Design, Formula and Calculation at Engineers Edge
Strength Properties of Metals at EngineersEdge.com
The Tempering of Martensite
Types of bolts and screw heads.
Fastener types.
Fasteners 101
Home Depot Special Order Fasteners at CrownBolt.com

"The Nuts and Bolts of Bolting" by Joseph C. Dille
Fastners 101
Metallurgy for the Non-Engineer

Gardner-Westcott is a bolt manufacturer.

Pozidriv™ is a trademark of European Industrial Services Ltd.
Pozidriv® is a registered trademarks of Phillips Screw Co.
Torx® is a reg. trademark of Camcar-Textron Inc. USA

last updated 1 Oct 2008