The invention relates to a tap changer for switching among different winding taps of a step transformer without interruption according to the preamble of the first patent claim. The general inventive concept lies in proposing a contact unit comprising several identically constructed contact carriers, which can assembled among each other by simple plugging to form a finished contact unit, wherein the individual contact carriers can each be fixed to the switching shaft by means of a bowed clamp and wherein furthermore at least two specially geometrically formed pins are provided as rotation-preventing elements on each contact carrier, on the side facing the switching shaft, which pins can be brought into engagement in the blind holes provided in the switching shaft in such a way that the entire contact unit is thus secured against rotation.