Abstract: A transmission or mechanical gearing for roller blinds or gates, window shades and awnings or the like, with a self-locking worm gear drive in a two part housing on one end of a shaft and an abutment for limiting of the number of rotations of the shaft in the unwinding direction. The abutment comprises an abutment pinion with the teeth number (n), the abutment pinion meshing with the worm wheel, a locking disc with the tooth number (n-1), the locking disc likewise meshing with the worm wheel, the locking disc being mounted coaxial to the abutment pinion, and an axially moveable abutment pin arranged in the abutment pinion, the abutment pin being prestressed with a spring and by means of a slot in the locking disc is able to engage in a double-sided abutment in the housing.