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Fastener Chess
This webpage is unique in that it combines information on the many types of fasteners with information on how to determine their strengths. This extends to joint strengths as well since the parts being fastened together are often weaker than the fastener itself. This is especially true when the objects are relatively thin sheets of metal, a common occurance in aircraft.

The page begins by reviewing the many fastener categories, focusing on those used in the American aircraft industry. It progresses to........., and concludes with fastener and joint strength analysis methods.

The Difference Between a Bolt and a Screw

A bolt is designed to be inserted through a smooth hole and secured with a nut, while a screw is designed to be used in a threaded hole—sometimes along with a nut. To learn more, see the American Society of Mechanical Engineers (ASME) standard B18.2.1 (1996).

Fastener Standards

Bolt Dimensions
AN - Air Force / Navy Standards
NAS - National Aerospace Standards
MS - Military Standards
AMS   -   Aeronautical Material Specifications
SAE - Society of Automotive Engineers
MIL - Military Specifications

Types of Fasteners

Sheet metal screw, hex head
Sheet metal screw, Phillips oval head

Hex bolt
Full thread hex bolt

Wood Screws
Screws with a smooth shank and tapered point for use in wood.
Abbreviated WS

Sheet Metal Screws
Fully threaded screws with a point for use in sheet metal.
Abbreviated SMS

Machine Screws
Screws with threads for use with a nut or tapped hole.
Abbreviated MS

Hex Bolts
Bolts with a hexagonal head with threads for use with a nut or tapped hole. Abbreviated HHMB or HXBT

Carriage bolt

Lag bolt

Wire Eye Bolt

Wire Eye Lag

Carriage Bolts
Bolts with a smooth rounded head that has a small square section underneath.

Lag Bolts
Bolts with a wood thread
and pointed tip.
Abbreviated Lag
Eye Bolts
A bolt with a circular ring on the head end. Used for attaching rope or chain.
Eye Lags
Similar to an eye bolt but with wood threads instead of machine thread.


Bolts in U shape for attaching to pipe or other round surfaces. Also available with a square bend.
J shaped bolts are used for tie-downs or as an open eye bolt.

Head Styles

Flat HeadFlat Head Profile Oval HeadOval Head Profile Pan HeadPan Head Profile Truss HeadTruss Head Profile
A countersunk head with a flat top.
Abbreviated FH
A countersunk head with a rounded top.
Abbreviated OH or OV
A slightly rounded head with short vertical sides.
Abbreviated PN

An extra wide head with a rounded top.

Round HeadRound Head Profile Hex HeadHex Head Profile Hex Washer HeadHex Washer Head Profile Slotted Hex HeadSlotted Hex Head Profile

A domed head.
Abbreviated RH

A hexagonal Head.
Abbreviated HH or HX
Hex Washer
A hex head with built
in washer.
Slotted Hex Washer
A hex head with built in washer and a slot.
Socket CapSocket Cap Profile Button HeadButton Head Profile    

Socket Cap
A small cylindrical head using a socket drive.

A low profile rounded head using a socket drive.

Tension Bolt Markings and Strength

Blah, Blah, Blah...

Head Marking Grade and
Nominal Size Range
Mechanical Properties
   Proof    Load
Min. Yield Strength
Min. Tensile Strength
Grade 2 head marking
No Markings

Grade 2

Low or medium carbon steel

1/4 thru 3/4 55,000 57,000 74,000
>3/4 thru 1-1/2 33,000 36,000 60,000
Grade 5 head marking
3 Radial Lines

Grade 5

Medium Carbon Steel, Quenched and Tempered

1/4 thru 1 85,000 92,000 120,000
>1 thru 1-1/2 74,000 81,000 105,000
Grade 8 head marking
6 Radial Lines

Grade 8

Medium Carbon Alloy Steel, Quenched and Tempered

1/4 thru 1-1/2 120,000 130,000 150,000
Stainless markings vary. Most stainless is non-magnetic

18-8 Stainless

Steel alloy with 17-19% Chromium and 8-13% Nickel

1/4 thru 5/8   40,000 Min. 80,000 – 90,000 Typical 100,000 – 125,000 Typical
3/4 thru 1   40,000 Min. 45,000 – 70,000 Typical 100,000 Typical
Above 1   80,000 – 90,000 Typical

Proof Load: Tensile load which the bolt must withstand without any evidence of permanent set.

Yield Strength: Load at which the bolt exhibits a specific permanent deformation.

Tensile Strength: Maximum tensile load which the bolt can withstand before breaking or failing.


\[ R = {\rho \; L \over A} \]

Theoretical Gauge Factor Values

It turns out that gauge factors can be estimated from the \(R = \rho L / A\) relationship by first determining \(dR/dL\) as follows

Electrical Circuits - Wheatstone Bridge

Strain Gauge Circuit


Many photographs and sketches shown here were taken from the internet and found via Google searches. Each such image has been referenced in order to give credit to its source. I especially want to acknowledge as a primary source of information here.

Also, thanks very much to Chuck Boulware and Bill Dunmon for contributing to this page.