A rack is a mechanical part that cooperates with a gear and is used for transmission. It is divided into spur gear rack and helical gear rack, which are paired with spur gear and helical gear respectively. Rack and pinion transmission is a transmission method in which gears and racks cooperate. When the gear is active, the rotary motion can be turned into a linear motion; when the rack is active, the linear motion can be turned into a rotary motion. Rack and pinion drives can be used in elevators, track systems, automotive steering systems, machine tools and feed mechanisms for actuators and other fields.