Cotter Pins

Cotter pins, also called split pins, are simple bend-to-lock fasteners that secure castle nuts, clevis pins, and shaft components against loosening or falling out. Inserted through a drilled hole and bent open, they provide cheap, reliable, tamper-evident retention. They're everywhere in machinery, automotive, and equipment. We stock cotter pins in steel and stainless across all common sizes.

How Cotter Pins Work

The pin is pushed through a cross-drilled hole — in a bolt, shaft, or clevis — and its two legs are bent apart so it can't back out. To remove, the legs are straightened and the pin is pulled. This makes cotter pins a positive mechanical lock that's easy to inspect and replace, commonly used with slotted (castle) nuts on axles and steering components.

Common Uses

Securing castle and slotted nuts on axles and tie rods, retaining clevis pins in linkages, and locking shaft collars and hardware. The bent legs provide visual confirmation the pin is engaged — important for safety-critical retention.

Materials and Finishes

Low carbon steel with zinc plating: the economical standard, soft enough to bend easily. 18-8 stainless: corrosion resistance for outdoor, marine, and corrosive environments. Choose by environment; stainless is essential where rust would seize or weaken the pin.

Dimensional Standards

Cotter pins conform to ASME B18.8.1 (inch) and DIN 94 / ISO 1234 (metric), sized by pin diameter and length.

Selecting the Right Cotter Pin

Match the pin diameter to the drilled hole and the length so the legs extend enough to bend fully around the nut or shaft. Choose stainless for corrosion resistance, steel for economy. Always use a new cotter pin on reassembly — a reused, fatigued pin can break. Bend both legs securely for positive retention.

Use the filters to narrow by diameter, length, and material.