The spindle (1) is joined to a coupling component (2) whose integrated cage contains balls which are forced into their active setting in the working plane by a piston-ringed (9) pressure bolt (5). The helically toothed spur gear (4) has at least three inside axial grooves (15) whose inside diameter matches the outside diameter of the cage (3). The bolt is guided within the cage bore by piston rings (9,10), using a cone transition piece (14) between the bolt and upper ring (9). The bolt can be guided onto a compression spring (11) in the upper part of the cage and is actuated by a lever (6) as joined to a Bowden cable. The drive passes between the worm gear and the spindle via the spur gear, using three radial holes in the cage in the groove area. The pressure bolt can have two different outside diameters as formed by the two rings of larger diameter which (a) in turn goes over conically into the pressure bolt.
