Rack and pinion

A gear mechanism in which a circular pinion meshes with a straight toothed rack, converting rotation into linear motion or vice versa.

Pinion: A small circular gear that meshes with another gear or a toothed rack. Its rotation drives the rack along its straight path.
Rack-and-pinion steering: A vehicle steering system that uses a pinion to move a transverse rack connected to the wheels. It is the best-known use of the mechanism in everyday vehicles.
Gear: A toothed machine element that transmits motion and force by engaging another toothed element. The pinion is a gear, while the rack extends gear teeth along a straight line.
Lead screw: A threaded shaft that converts rotation into linear movement through a mating nut. It also produces linear travel, but uses screw threads rather than meshing teeth.
Gear module: A measure of gear-tooth size equal to pitch diameter divided by tooth count. Matching module gives rack and pinion teeth compatible spacing.
CNC router: A computer-controlled machine that cuts material with a rotating tool along programmed paths. Rack drives can move its cutting gantry over long distances.
Rotational motion: Motion in which an object turns around an axis. The pinion supplies the rotating input in one common operating mode.
Ball screw: A screw drive that uses recirculating balls between a threaded shaft and nut. It offers low-friction linear motion where rack drives may be preferred for long travel.
Pitch line: An ideal line on a gear or rack where rolling contact is represented without slipping. It relates pinion rotation to rack displacement.
Linear actuator: A device that produces motion in a straight line. A rack and pinion is one way to create mechanical linear actuation.

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