Linchpin
（重定向自Linch pin）
![A linchpin with an integral spring retainer](/Images/godic/202501/24/Lynch-pin0845.jpg")
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 14th century and derives from Middle English elements meaning "axletree pin".