What is a traditional fastener which prevents a wheel from coming off its axle, and refers metaphorically to a crucial person or part?
Linchpin together." Linchpin 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". Securing implements onto the three-point hitch of a tractor is an example of application. Linchpins may also be used in place of an R-clip for securing hitch pins. The word "linchpin" is also used figuratively to mean "something [or someone] that holds the various elements of a complicated
Wheel and axle with a drive force applied tangentially to the perimeter of the wheel and a load force applied to the axle, respectively, that are balanced around the hinge which is the fulcrum. The mechanical advantage of the wheel and axle is the ratio of the distances from the fulcrum to the applied loads, or what is the same thing the ratio of the diameter of the wheel and axle. A major application is in wheeled vehicles, in which the wheel and axle are used to reduce friction of the moving vehicle with the ground. Other examples of devices which use the