All the foregoing clutches present in one form or another very complicated devices for freeing the transmission shaft from the engine shaft, but the magnetic clutch is a device which has simplicity for its foremost argument. The magnetic clutch, consists primarily of three parts: the field, usually in the form of a ring; the armature always of ring shape; and the oil casing shaped to accommodate the other parts, its function being that of a cover, simply. The armature is a simple cast-iron plate of rectangular section, adapted to be drawn into engagement with the field, when the latter is energized.

The field, on the other hand, is made up of the back plate, the inner and outer field rings, the magnetizing coil and the contact rings. In operation, the accelerator is energized by closing the electrical circuit, which sends a current through the field. This magnetism attracts the armature, which then moves laterally, closing the very small gap between the two. The oil in which the whole clutch works prevents it from taking hold suddenly, or gripping, but as this oil film on the two surfaces is gradually squeezed out, the clutch as gradually takes hold.