An inductive sensor including a casing in which are positioned: a ferromagnetic core having a U shape, which core includes two external branches and a transverse branch linking the two branches; two detection coils disposed respectively on the external branches of the core; a calibration mechanism positioned between the two external branches of the magnetic core, a longitudinal positioning of the calibration mechanism with respect to an end of the external branches being adjustable; an intermediate fixing piece for fastening the calibration mechanism onto the ferromagnetic core, the intermediate fixing piece being placed forcibly in an opening made in the transverse branch, the calibration mechanism including a threaded zone configured to be screwed into a smooth hole made in the intermediate fixing piece.