Worm gearing can reduce the rotational speed or allow higher torque to be transmitted, they are a compact way of achieving this.   The addition of a worm drive to a small high-speed motor increases the range of applications that it is suitable for.   The worm acts as a screw, the form on the mating wormwheel is similar in appearance to a spur gear but has a lead angle the same as the screw (worm).

A single start worm, once engaged with its wheel, rotating through 360 degrees only advances the wormwheel by one tooth, therefore a single start worm running with a 50 tooth wheel creates a ratio of 50:1