guiding elements 11 and 12 extend in each case with uniform incrementation or pitch over an angle range of 360 u00b0 this also need not essentially be the case it would also suffice if either the first or the second guiding element 11 12 were to have only one ridge or only one recess this too would ensure a rotation resistant arrangement of the index elements 4 on the coupling part 3 in fig4 by pulling off the coupling part 3 the adjustment disk 24 and locking disk 22 otherwise arranged lying inside in the coupling part can be seen these also bear toothings which engage with an internal toothing 26 not visible in fig4 of the coupling part 3 when pushed on i e when the coupling part 3 is inserted on and engages the adjustment disk 24 and locking disk 22 the mode of operation of the transmission device 7 chosen in this embodiment for transmitting a rotary movement of the coupling part 3 onto the spindle 14 is now described with the help of the sectional representation according to fig2 in the pushed on fitted and engaged state represented in this figure the cover 6 the coupling part 3 and the index elements 4 are connected rotation resistantly to one another via a toothing 26 this also applies to the adjustment disk 24 and the locking disk 22 the adjustment disk 24 is in turn connected rotation resistantly via a toothing 25 to a nut 17 by means of the snap action connection 28 the coupling part 3 rests in a corresponding recess of the nut 17 the screw 8 for.