AskDefine | Define cotter

Dictionary Definition



1 a peasant farmer in the Scottish highlands [syn: cottar]
2 a medieval English villein [syn: cottier]
3 fastener consisting of a wedge or pin inserted through a slot to hold two other pieces together [syn: cottar]

User Contributed Dictionary



Etymology 1


  1. In the context of "mechanical engineering": A pin or wedge inserted through a slot to hold machine parts together.
  2. Erroneously, sometimes used of a cotter pin.
Usage notes
The terms cotter and "cotter pin" are sometimes used interchangeably, although they have different functions. Basically a cotter holds parts together and a "cotter pin" holds the cotter in its place. For a more detailed explanation see Wikipedia articles on w cotter and w cotter pin.
pin to hold parts together
  • Finnish: tappi
cotter pin
  • Finnish: sokka
Related terms

Etymology 2

Alternative spellings


  1. A peasant who performed labour in exchange for the right to live in a cottage.
  • Finnish: torppari

Extensive Definition

In mechanical engineering a cotter is a pin or wedge passing through a hole to fix parts tightly together.
Typical applications are in fixing a crank to its crankshaft, as in a bicycle, or a piston rod to a crosshead, as in a steam engine.

Popular Usage

Formerly, it was common to mount bicycle crank arms using a cotter, though now usually a more easily maintained arrangement is used such as a square tapered or splined interface. These cotters have a short threaded section at the narrower end of the taper, which is used to hold the cotter in place with a washer and nut.
Cotters in bicycles are frequently referred to as cotter pins, which correctly refers to a split pin, so named for its use in retaining a cotter. Because bicycle cotters were normally retained by a nut and washer, the distinction was unimportant in this context.
In other contexts, the distinction is important: a cotter is intended to take considerable shear loads, while a cotter pin is not, having to be soft enough to allow it to secured by being bent.

See also

cotter in German: Keil (Technik)

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