First and second sets of grooves define first and second sets of elongate projections which are respectively subject to compression and elongation when the shaft in which they are defined, is subject to torque. Two yoked coils which are excited with an alternating current, are each disposed close to a set of projections. The compression and elongation of the projections changes the amount of magnetic flux which flows along the projections and therefore the inductance of the coils. The coils form part of a bridge circuit which is sensitive to the change in inductance in a manner which enables the amount of torque to be measured.