Rack is a special gear with teeth distributed on a bar body. Rack is also divided into straight rack and helical rack, respectively, and spur gear and helical gear pair use; The tooth profile of the rack is straight rather than involute (or flat for the tooth surface), which is equivalent to a cylindrical gear with an infinite radius of the dividing circle.

The main parameters of the rack are: the width of the tooth groove, the height of the tooth top, the height of the tooth root, the height of the tooth, the thickness of the tooth, the radius of the tooth root, etc.