Worm gears are used when huge Coupling equipment reductions are needed. It is common for worm gears to possess reductions of 20:1, and actually up to 300:1 or greater.
Many worm gears have an interesting property that no additional gear set has: the worm can easily turn the gear, however the gear cannot turn the worm. This is because the position 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 pays to for machines such as conveyor systems, where the locking feature can act as a brake for the conveyor when the motor isn’t turning. An added very interesting usage of worm gears is definitely in the Torsen differential, which can be used on some high-performance cars and trucks.