Rack and pinion gears are made of a small round spur gear (the pinion) and a flat bar with evenly spaced teeth (the rack). Rack and pinion gears convert rotational motion into linear motion. As the pinion turns, its teeth mesh with the rack’s teeth to move it in a straight line.

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.

Rack and pinion gears are commonly used in automotive steering, meat processing, and rack railways, among other applications.