Worm gears are used when huge gear reductions are needed. It’s quite common for worm gears to have got reductions of 20:1, and even up to 300:1 or greater.

Many worm gears have an interesting property that no planetary gearbox additional gear arranged has: the worm can simply turn the gear, but the gear cannot turn the worm. This is because the angle on the worm is indeed shallow that when the gear tries to spin it, the friction between the gear and the worm keeps the worm in place.

This feature pays to for machines such as conveyor systems, in which the locking feature can become a brake for the conveyor when the motor is not turning. One other very interesting use of worm gears is usually in the Torsen differential, which is utilized on some high-performance vehicles.