Worm gears, also called worm drives, use a long, threaded cylinder called a worm that meshes with the teeth of a worm wheel (similar to a spur gear) to transmit motion. They can be used in a right-angle configuration. The worm wheel is unable to turn the worm, providing a built-in lock or a braking system. They are quieter than spur gears, low maintenance, and suitable in applications that require increased torque and reduced speed, or when changing the rotation direction.

Gears are available in a variety of materials, including stainless steel, cast iron, brass, and plastic, depending on application. There are several other factors to consider when selecting the appropriate gear for an application. The gear’s outside diameter is the longest linear distance across a gear. The bore diameter is the distance across the hole located in the center of a gear, where the mounting shaft will be inserted. The hub diameter is the distance from one tip of the shoulder (the hub) to the other. The thickness is the distance measured from the tip of a gear tooth to the gear’s bore or base (for a gear rack). The number of the teeth refers to the number of teeth around a gear. The pitch, also called the diametral pitch, is the number of teeth divided by the pitch diameter, and it can also serve as a guide for tooth size.

Worm gears are used in rolling mills, presses, elevator drives, and stringed instruments for tuning.