A caliper 2a is disposed between rotation input side and rotation output side engagement portions 8, 9 of a support member 3a so as to restrict the movement of the caliper 2a in a circumferential direction of a rotor 1. Since the door has a controllable height by being opened and closed, a moment arm becomes longer than when using the conventional tool such as a spanner. The rotor is made up of a unitary ceramic component, such as silicon carbide. The receiver circuit also includes a threshold detector with an input coupled to the output of the automatic gain controller and an output coupled to the switch for selecting between the filtered pathway and the short circuit pathway, thereby removing the filter from the signal path if not needed. The compositions are useful in paints and other coatings.