Worm gears are used when large gear reductions are needed. It is common for worm gears to possess reductions of 20:1, and also up to 300:1 or greater.
Many worm gears have an interesting property that no additional gear arranged has: the worm can simply turn the gear, however the gear cannot turn the worm. That is because the angle on the worm is indeed shallow that when the gear attempts to spin it, the friction between the equipment and the worm keeps the worm set up.
This feature is useful for machines such as for example conveyor systems, where the locking feature can become a brake for the conveyor when the motor isn’t turning. One other very interesting utilization of worm gears is planetary gearbox definitely in the Torsen differential, which is utilized on some high-performance vehicles.