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Gears are wheels, cylinders, or beveled cone-like rotating devices which transmit power and motion from one machine shaft to another, and are capable of changing speed, force, and direction. Gears commonly have teeth bordering the outer perimeter, which transfers… Learn More

Gears come in several types for use in different power transmission configurations and for different applications. Some common types of gears are spur gears, worm gears, and bevel and miter gears. Spur gears are simple cylindrical or disk-shaped gears with straight teeth that interconnect on parallel axes. Worm gears use a long, threaded cylinder called a worm that meshes with the wheels of a spur gear-like worm wheel to transmit motion in a right-angle configuration. Bevel and miter gears are conical-shaped gears which transmit power between two shafts positioned typically at a 90-degree angle (or less for some bevel gears). Examples of other types of gears are change gears, rack and pinion gears, helical gears, and internal gears. For all gear types, mating gears need to have the same diametral pitch and pressure angle; some types, however, must also have the same thread (worm gears), face width (bevel and miter gears), and helix angle (helical gears) in order to mate.

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.

Gears are commonly used to transmit power and motion in the agriculture, automotive, construction, mining, packaging, and power production industries, and can be found in a variety of machines, including bicycles, automobiles, clocks, elevators, rolling mills, and egg beaters.

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