revolutions i e limitation of displacement of the components driven by the pinion 3 the abutment means which are disposed on the one hand on the rose 7 and on the other hand on the toothed ring 16 will now be explained a blocking pin 19 slidably guided in the rose 7 parallel to the shaft 1 can best be seen from fig1 and 8 a cylindrical bore 20 in the rose 7 is closed to the outside by a lid 21 firmly connected to the rose 7 the lid is provided with an opening which guides the portion 22 of the blocking pin 19 extending out of the rose 7 the end of the blocking pin 19 provided with a transverse recess 23 is guided in a bore 24 in the rose 7 a helical compression spring 25 is inserted into the annular space between the blocking pin 19 and the cylindrical bore 20 and bears at one end against a flange 26 fixed to the blocking pin 19 and at the other end against the rose 7 the bore 24 is continued as far as an annular channel 27 concentrically surrounding the shaft 1 into which channel the blocking pin 19 penetrates a blocking ring 28 is set in the annular channel 27 being rotatably journalled with its inner surface 29 fig6 on an annular projection 30 of the rose 7 circumferential steps 31 and 32 fig2 are provided on and form the abutment means for the blocking ring 28 the annular shoulder 33 of the blocking ring 28 extending between the circumferential steps 31 and 32 is provided with a gap 34 for the passage of the blocking.