gears are simple cylindrical or disk-shaped gears with straight teeth
that interconnect on parallel axes to provide uniform rotary motion. They may
have a plain, hub, web, or spoke style, and they come in many variations, such
as gear racks, pinions, change gears, and internal gears. Spur gears are the
most common gear type, and are suitable for applications that require decreased
speed and high torque.
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.
Spur gears are used in speed control, packaging, and power plants applications, among others.