The primary advantage of worm gears is their ability to provide high reduction ratios and correspondingly high torque multiplication. They can even be applied as speed reducers in low- to medium-quickness applications. And, because their lowering ratio is based on the number of gear teeth by itself, they are smaller sized than other styles of gears. Like fine-pitch business lead screws, worm gears are typically self-locking, which makes them well suited for hoisting and lifting applications.
Although the sliding contact reduces efficiency, it provides extremely quiet operation. (The utilization of dissimilar metals for the worm and gear also plays a part in quiet operation.) This makes worm gears suitable for use where noise should be minimized, such as for 
example in elevators. In addition, the usage of a softer material for the gear means that it can absorb shock loads, like those experienced in serious equipment or crushing machines.
The meshing of the worm and the apparatus is an assortment of sliding and rolling actions, but sliding contact dominates at high reduction ratios. This sliding action causes friction and heat, which limits the effectiveness of worm gears to 30 to 50 percent. As a way to minimize friction (and for that reason, heat), the worm and gear are constructed of dissimilar metals – for instance, the worm may be made of hardened steel and the gear made of bronze or aluminum.
Such as a ball screw, the worm in a worm gear may well have a single start or multiple starts – and therefore there are multiple threads, or helicies, on the worm. For a single-start worm, each total turn (360 degrees) of the worm increases the gear by one tooth. Hence a gear with 24 teeth provides a gear reduction of 24:1. For a multi-start worm, the gear reduction equals the number of teeth on the gear, divided by the number of begins on the worm. (This is different from almost every other types of gears, where in fact the gear reduction is certainly a function of the diameters of both components.)
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