A linchpin, also spelled linch pin, lynchpin, or lynch pin, is a fastener used to prevent a wheel or other part from sliding off the axle upon which it is riding. The word is first attested in the late fourteenth century and derives from Middle English elements meaning "axletree pin".
The word "linchpin" is also used figuratively to mean "something [or someone] that holds the various elements of a complicated structure together".
- Circle cotter – Ring type of retaining component
- Circlip – Type of fastener or retaining ring
- Cotter (pin) – Pin or wedge passing through a hole to fix parts tightly together
- Hairpin clip
- Kingpin (automotive part) – Main pivot in a vehicle's steering mechanism, or part of the fifth wheel coupling for a semi truck
- R-clip – Type of fastener made of a springy material
- Split pin – Metal fastener with two tines that are bent during installation
- Spring pin
- "linch-pin, n.". OED Online. June 2014. Oxford University Press. http://www.oed.com/view/Entry/108578 (accessed August 25, 2014; now behind paywall).
- "linchpin (n.)". Online Etymology Dictionary. https://www.etymonline.com/word/linchpin (accessed 1 June 2018).
- "Hitch Pins and Linch Pins Information on GlobalSpec". Archived from the original on 2010-08-18.
- "Linchpin". Dictionary.reference.com. Retrieved 2012-03-24.