Shear pin

A shear pin is a mechanical detail designed to allow a specific outcome to occur once a predetermined force is applied.

They are most commonly used in drive trains, such as a snow blower's auger or the propellers attached to marine engines.

The design may be such that the shear pin will have several different causes of failure – towbar rotation about its long axis, sudden braking or acceleration, excessive steering force, etc.

Additionally, shear-pins are frequently used in anti-tank mine fuzes, to prevent them from being triggered by much lighter, non-target vehicles such as motorcycles.

Typically, the shear-pin in an anti-tank mine is designed to snap (and release the spring-loaded firing pin) when a weight in excess of 1500 kilograms is applied to the pressure plate.

This can for example be achieved by giving the material a high degree of elasticity so that, like a spring, the metal returns to its original shape after being deformed by an external force.

A shear pin however is often tempered to make the metal brittle, so that it breaks or shatters rather than bends when the required force is applied.