20 running all round in the manner of a gearwheel and the sliding pieces 17 have only a few coupling teeth 21 three of these in fig3 in an extreme case a single tooth is sufficient the whole of the sliding pieces 17 distributed uniformly over the circumference is held together and pressed outward by a looping spring 22 which is a closed bent ring consisting of a spring wire a shift sleeve 23 is displaceable in the axial direction on the bush 18 for this purpose said shift sleeve has for example a peripheral groove 24 for the engagement of a shift fork or other actuator not illustrated the shift sleeve 23 has a part 26 which diverges in a bell shaped manner and the inner face 25 of which is designed conically the inner face 25 cooperates with the sliding pieces 17 for the engagement of the sliding pieces 17 the shift sleeve 23 is displaced in the axial direction in such a way that the conical inner face 25 pushes the sliding pieces 17 inward with the result that their teeth 21 are pressed into the coupling toothing 20 of the bush between the output pinion 7 and the intermediate part 14 is arranged a compression spring 27 which endeavors to push the intermediate part 14 away from the first clutch half 11 the bush 18 is limited in its axial.