Worm gears are used when large gear reductions are needed. It is common for worm gears to possess reductions of 20:1, and actually up to 300:1 or Motorbase greater.
Many worm gears have a fascinating property that no other gear arranged has: the worm can certainly turn the gear, but the gear cannot turn the worm. This is because the angle on the worm is indeed shallow that when the apparatus attempts to spin it, the friction between your equipment and the worm keeps the worm in place.
This feature pays to for machines such as conveyor systems, in which the locking feature can act as a brake for the conveyor when the motor isn’t turning. An added very interesting use of worm gears is certainly in the Torsen differential, which is used on some high-performance cars and trucks.