A captive float nut comprising a nut body having a threaded aperture defined there-through for receiving a threaded shaft. One or more of the handle section, the head section, and the connecting section include a superelastic metal. The independent processing systems may have more than one CPU. The voltage difference between a voltage detected by the detection resistors 18, 20 and a reference voltage obtained from a point of connection 35 between the voltage dividing resistors is input to two Op-Amps 36, 38 serving as the input voltage. The control device comprises a detector adapted to detect the phase-shift between the periodic square-wave signal generated by the generating means and the current flowing through the resonant circuit, and adapted to control the turning off of the half-bridge when the phase-shift exceeds a first phase-shift value. A target area is identified midway between the left edge and the right edge.