Cotter (pin)

Cross-section of a connecting rod, showing strap (S), gib (G), and cotter pin (C)
Another view, with scale, of bicycle crank cotter

A cotter is a pin or wedge with a flat bearing surface passing through a hole to fix parts tightly together. In British usage cotter pin has the same meaning,[1] but in the U.S. it means a split pin.

Typical applications are in fixing a crank to its crankshaft, as in a bicycle, and a piston rod to a crosshead, as in a steam engine. The angle of the wedge determines the position of the parts being held; therefore, on a bicycle, the pedal arms will only be at 180 degrees to each other if the angle of the cotter pin's wedge is the same on both pins.

  1. ^ Van der Plas, Rob (1993), The Bicycle Repair Book: The New Complete Manual of Bicycle Care (2nd ed.), MBI Publishing Company, p. 66, ISBN 978-0-933201-55-2[permanent dead link‍].