Cotter Pin Dimensions according to ASME B18.8.1 standard. All dimensions are in inches.

The cotter pins are intended for use with clevis pins and in pinned bolt and nut assemblies or other type of free fitting pinned assemblies in general applications.

Some important notes from the ASME standard:

- The preferred point type shall be the extended prong - square cut or hammer lock designs.

- The misalignment of prongs over entire length of shank shall not stop pin from being inserted into the gauging hole.

- Materials: Low carbon steel. Pins may also be made from ASTM A493, Types 302 (UNS S30200) and 304 (UNS S30400), corrosion resistant steel; ASTM B134, Alloy 260 (UNS C26000), cartridge brass; Monel Alloy (UNS N04400)

- Each prong of the cotter pin shall be capable of withstanding being bent back upon itself once, with no visible indication of fracture occurring at the point of bend.

- Cotter pins are manufactured from approximately half-round wire

- Designation: Name, Nominal Size, Pin Length, Point Type, Material and Finish. Ex: Pin, Cotter, 1/8 x 1, Extended Prong Type, Steel, Zinc Plated

Cotter Pin Dimensions:

Point Type 
Nominal Pin Size
Pin Length *

Note * : Preferred lengths advised in ASME B18.8.1 standard.


Cotter Pins Dimensions
Parameter Value (inch)
Nominal Size (Basic Pin Dia.) ---
Nominal Size (Basic Pin Dia) ---
Max. Total Shank Diameter [Amax] ---
Min. Total Shank Diameter [Amin] ---
Maximum Wire Width [Bmax] ---
Minimum Wire Width [Bmin] ---
Minimum Head Diameter [Cmin] ---
Extended Prong Length [Dmin] ---
Gage Hole Diameter (+/- 0.001) ---
Maximum Pin Length [Lmax] ---
Nominal Pin Length [Lnom] ---
Minimum Pin Length [Lmin] ---

Note: Total shank diameter (A) is 2 times wire thickness which is measured at the end of the cotter pin.


Clevis Pin: A type of cylindrical pin with a head at one end and with a hole passes through the diameter at the other end. A clevis pin is generally locked in place with a cotter pin. Clevis pins provide rotation between connected components about pin axis.


Link Usage
Cotter pin sizes chart Tabulated form of the cotter pin dimensions calculator.


  • ASME B18.8.1-1994, Clevis Pins and Cotter Pins (Inch Series)
  • Oberg.E , Jones.D.J., Holbrook L.H, Ryffel H.H., (2012) . Machinery's Handbook. 29th edition.  Industrial Press Inc. , pp 1746
  • Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2016) . Machinery's Handbook . 30th edition.  Industrial Press Inc. , pp 1796