direction of the axis 31 causes the activating element 32 to move back into the passive position 2 by way of a lifting movement at the same time the spring element 23 pushes the wings 33 in the drawing plane into the second pair of grooves 12 b as a result of which a locking connection of the bearing point 30 in the link 13 is produced during this movement of the activating element 32 back into the passive position 2 the driver 34 simultaneously leaves the recess 36 of the bearing point 30 in this way the operative position 5 according to fig1 and fig3 is reached in an alternative of the invention the recess 36 and or the driver 34 is designed in such a way that in each position 2 3 of the activating element 32 the driver 34 is in the recess 36 when at this point the user would like to move the key portion 20 out of the operative position 5 into the inoperative position 4 the activating element 32 must be reactuated again then the activating element 32 leaves via a lifting movement its passive position 2 in the direction of the active position 3 in the course of which the wings 33 leave the second pair of grooves 12 b and at the same time the driver 34 moves into the recess 36 of the bearing point 30 since the spring element 23 exerts according to fig3 a torque on the activating element 32 in the counterclockwise direction it is necessary for the user to exert a corresponding force larger than the opposing torque on the key portion 20.