screw in spindle 5 is interrupted a clutch 6 which is arranged in the drive chain between the drive motor 2 and the hollow spindle 3 has a screw in side first clutch member 7 fixedly connected with the hollow spindle 3 and a second axially displaceable and freely rotatable clutch member 8 the first clutch member 7 is displaceable against a biasing force of a first spring 9 in a direction opposite to the screw in direction toward the second clutch member 8 the second clutch member 8 is displaceable against a biasing force of a second spring 10 also in the direction opposite the screw in direction toward the gear 11 of the gear unit 24 through which the hollow spindle 3 extends the gear 11 is drivingly connected with the output shaft 19 of the drive motor 2 behind the hollow spindle 3 and coaxially therewith there is located a coil of an electromagnet 17 an impact mass 15 which is displaceable parallel to the screw in direction and has a hardened insert 6 embedded therein is arranged in the coil of the electromagnet 17 the hardened insert 16 which cooperates with the rounded impact surface of the screw in spindle 5 can be formed e g as a cylindrical pin the insert 16 transmits the impact energy of the impact mass 15 to the screw in spindle 5 in the embodiment shown in the drawings the impact mass 15 is retained in its initial position.