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

Many worm gears have an interesting property that no various other gear established has: the worm can certainly turn the gear, but the gear cannot turn the worm. That is because the position on the worm is indeed shallow that when the gear tries to spin it, the friction between your gear and the worm retains the worm set up.

This feature is useful for machines such as conveyor systems, where the locking feature can act as a brake for the conveyor when the motor is not turning. An added very interesting usage of worm gears is definitely in the Torsen differential, which is used on some high-performance cars and Taper Lock Pulley trucks.