Worm gears resemble screws. A worm gear is usually meshed with an ordinary looking, disk-shaped gear, which is called the gear, wheel, or worm wheel. Worm and gear sets are a simple and compact way to achieve a high gear ratio. For example, helical gears are normally limited to gear ratios of less than 10:1 while worm gear sets vary from 10:1 to 500:1. A disadvantage is the potential for considerable sliding action, leading to low efficiency. Worm gears can be considered a species of helical gear, but its helix angle is usually somewhat large (close to 90 degrees) and its body is usually fairly long in the axial direction; and it is these attributes which give it its screw like qualities.

Worm gears resemble screws. A worm gear is usually meshed with an ordinary looking, disk-shaped gear, which is called the gear, wheel, or worm wheel. Worm and gear sets are a simple and compact way to achieve a high gear ratio. For example, helical gears are normally limited to gear ratios of less than 10:1 while worm gear sets vary from 10:1 to 500:1. A disadvantage is the potential for considerable sliding action, leading to low efficiency. Worm gears can be considered a species of helical gear, but its helix angle is usually somewhat large (close to 90 degrees) and its body is usually fairly long in the axial direction; and it is these attributes which give it its screw like qualities.