A current-carrying coil in non-uniform magnetic field is subjected to magnetic force and magnetic moment, it commits rotation other than translation.

This paper put forward the moment of magnetic force acted on current-carrying coil in even magnetic fied is revolving of regular axle and the method of determined the place of revolving axle.

The probe comprises an eddy current coil and a support means for carrying the coil in an orientation suitable for introducing eddy currents into material directly beneath a raised-head fastener.