The worm wheel pairs presented in the figure indicate a varying slope over their length and can be axially displaced against a spring. At low loads, the slope associated with low losses comes into play such that as a result of the low number of gear wheel pairs meshed with the spur gears, the compensation is hardly affected. If the input torque increases, the worm wheels are displaced in the direction of the friction-intensive lead angles as a result of increasing circumferential forces. Locking values of about 90% are achieved.