Worm gears are used when huge equipment reductions are needed. It’s quite common for worm gears to have got reductions of 20:1, and Taper Pulleys actually up to 300:1 or greater.
Many worm gears have a fascinating property that no additional gear established has: the worm can easily turn the gear, however the gear cannot turn the worm. This is because the angle on the worm is so shallow that when the apparatus tries to spin it, the friction between your gear and the worm retains the worm set up.
This feature pays to for machines such as for example conveyor systems, in which the locking feature can become a brake for the conveyor when the motor isn’t turning. An added very interesting use of worm gears is definitely in the Torsen differential, 
which is used on some high-performance vehicles.