The shear pin cartridge coupling is a Series H Mill type coupling. It is designed to disconnect the driving and driven equipment during torque overload. The purpose of the design is to prevent damage to the equipment- motor, gearbox, pump, etc. from torque overload. FAST’S® Mill Shear pin couplings are used to limit the peak torque to a predetermined safe value. This value is greater than the normal starting torque of the system.