The primary advantage of worm gears is their ability to provide high reduction ratios and correspondingly high torque multiplication. They can even be employed as velocity reducers in low- to medium-swiftness applications. And, because their lowering ratio is based on the amount of gear teeth by itself, they are smaller sized than other styles of gears. Like fine-pitch lead screws, worm gears are typically self-locking, which makes them perfect for hoisting and lifting applications.
Although the sliding contact decreases efficiency, it provides very quiet operation. (The utilization of dissimilar metals for the worm and gear also contributes to quiet operation.) This makes worm gears suitable for use where sound should be minimized, such as for example in elevators. In addition, the application of a softer material for the gear means that it can absorb shock loads, like those experienced in hefty equipment or crushing machines.
The meshing of the worm and the gear is an assortment of sliding and rolling actions, but sliding contact dominates at high reduction ratios. This sliding action causes friction and warmth, which limits the effectiveness of worm gears to 30 to 50 percent. So as to minimize friction (and therefore, heat), the worm and gear are created from dissimilar metals – for example, 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 could have a single start or multiple starts – meaning that there are multiple threads, or helicies, on the worm. For a single-start worm, each total change (360 degrees) of 
the worm increases the gear by one tooth. Consequently a gear with 24 teeth will provide a gear reduced amount of 24:1. For a multi-start worm, the gear reduction equals the number of teeth on the apparatus, 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 can be a function of the diameters of both components.)
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