Shear pin

(design engineering) A pin or wire provided in a fuse design to hold parts in a fixed relationship until forces are exerted on one or more of the parts which cause shearing of the pin or wire; the shearing is usually accomplished by setback or set forward (impact) forces; the shear member may be augmented during transportation by an additional safety device. In a propellant-actuated device, a locking member which is released by shearing. In a power train, such as a winch, any pin, as through a gear and shaft, which is designed to fail at a predetermined force in order to protect a mechanism.

A shear pin is the mechanical sacrificial part, analogue of an electric fuse. Installed in a drive train, it is designed to break in the case of a mechanical overload, preventing other, more-expensive parts of the drive train from being damaged.

A shear pin may be plain metal rod inserted through a hub and axle; the diameter of the rod is carefully chosen to allow the shearing action when the desired breakaway force or shock is reached. A cotter pin may also be used as a low-tech shear pin.

A common use of shear pins is in the drive train of a snow blower's auger or the propellers attached to marine engines.

See also

• Bolted joint

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