This unit is composed of two major parts. The first part is the core, mandatory driving, integral with two fly-weights and return springs. The second part is the drum connected to the driven part (clutch assembly) or to a fixed part (brake assembly).

The acceleration of the driving shaft and thus of the core applies a stress to fly-weights. Up to a given speed shown on the table of characteristics, the return springs compensate for the action of the centrifugal force. Beyond “nil torque” speed, the fly-weights move apart from each other, then come into contact with drum. The transmitted torque is a function of the rotational speed.