Racks and pinions are power-transmission components primarily used for converting rotary to linear motion and vice versa. The rack is a linear gear, flat or rod-shaped, which, when meshed with a small cylindrical gear (the pinion), is used in mechanical engineering for converting rotary to continuous linear motion and vice versa.

A gear rack has either straight teeth cut into one surface of a square or round section of rod, or helical teeth.

The latter guarantee a decidedly greater working surface and thrust compared to the former, so they are best suited in those sectors requiring greater impetus from gears and the engines themselves (such as agricultural machinery), or in case of skewed or even orthogonal shafts.