A cotter pin, also known as a split pin, is a metal fastener with two tines that are bent during installation. Typically made of thick wire with a half-circular cross section, split pins come in multiple sizes and types.
Cotter Pins Applications
Cotter pins are most commonly used to lock castle and slotted nuts or secure a clevis pins as well as wheel or machine components on an axle. Cotter pins are easy to install and remove. A split pin has two long tines that are bent to hold it in place. Hairpin clips, also called r clips, are designed to slip on with no bending required.
American cotter (split) pin sizes |
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| Nominal diameter | Hole size | For bolt size | |||
| in | mm | in | mm | in | mm |
| 1⁄32 | 0.79 | 3⁄64 | 1.19 | ||
| 3⁄64 | 1.19 | 1⁄16 | 1.59 | ||
| 1⁄16 | 1.59 | 5⁄64 | 1.98 | 1⁄4 | 6.35 |
| 5⁄64 | 1.98 | 3⁄32 | 2.38 | 5⁄16 | 7.94 |
| 3⁄32 | 2.38 | 7⁄64 | 2.78 | 3⁄8 | 9.53 |
| 7⁄64 | 2.78 | 1⁄8 | 3.18 | ||
| 1⁄8 | 3.18 | 9⁄64 | 3.57 | 1⁄2 | 12.70 |
| 9⁄64 | 3.57 | 5⁄32 | 3.97 | 5⁄8 | 15.88 |
| 5⁄32 | 3.97 | 11⁄64 | 4.37 | 3⁄4 | 19.05 |
| 3⁄16 | 4.76 | 13⁄64 | 5.16 | 1, 1 1⁄8 | 25.4, 28.58 |
| 7⁄32 | 5.56 | 15⁄64 | 5.95 | 1 1⁄4, 1 3⁄8 | 31.75, 34.93 |
| 1⁄4 | 6.35 | 17⁄64 | 6.75 | 1 1⁄2 | 38.10 |
| 5⁄16 | 7.94 | 5⁄16 | 7.94 | 1 3⁄4 | 44.45 |
| 3⁄8 | 9.53 | 3⁄8 | 9.53 | ||
| 7⁄16 | 11.11 | 7⁄16 | 11.11 | ||
| 1⁄2 | 12.70 | 1⁄2 | 12.70 | ||
| 5⁄8 | 15.88 | 5⁄8 | 15.88 | ||
| 3⁄4 | 19.05 | 3⁄4 | 19.05 | ||