Worm gears are used when large equipment reductions are needed. It is common for worm gears to have reductions of 20:1, and actually up to 300:1 or greater.

Many worm gears have an interesting property that no additional gear arranged has: the worm can simply turn the gear, however the gear planetary gearbox cannot turn the worm. That is because the angle on the worm is so shallow that when the gear attempts to spin it, the friction between the equipment and the worm keeps the worm set up.

This feature is useful for machines such as conveyor systems, where the locking feature can become a brake for the conveyor when the motor isn’t turning. One other very interesting usage of worm gears is in the Torsen differential, which is used on some high-performance cars and trucks.