The driving worm shaft acts like a screw as it turns the worm gear. The geometry of the worm shaft and worm gear is unique and results in the following limitation: the worm shaft can turn the worm gear, but the worm gear cannot rotate the worm shaft. In contrast, other gear types can be operated in reverse. This one-way operation can be beneficial for some applications that only move in one direction (i.e. some conveyor belts).