Meshing with teeth on a small gear (the pinion), pinion and Rack, the mechanical device consists of a bar of rectangular cross-section (Gear Rack), having teeth on one side. Meshing with teeth on the rack that are inclined to the pinion-shaft axis, the pinion may have helical (twisted) teeth and straight teeth.

On their steering mechanisms, some automobiles have rack-and-pinion drives that operate in this way.

On a table guided on tracks parallel to the rack, if the rack is fixed and the pinion is carried in bearings and to the rack as shown by the arrow CD, rotation of the pinion shaft will move the table parallel. To obtain rapid movements of worktables, rack-and-pinion mechanisms are used in this way on machine tools; the pinion shaft is usually rotated with a hand crank.

Attached to a rotating shaft, the Gear, Motor base machine component consists of a toothed wheel. To modify and transmit rotary motion and torque (turning force) without slip, the teeth of one gear engaging the teeth on a mating gear, Gears operate in pairs. On circles, if the teeth on a pair of mating gears are arranged i.e., the ratios of the rotary torques and speeds of the shafts are constant if the gears are toothed wheels. The torque and speed ratios vary if the teeth are arranged on noncircular bodies.

Connecting must be relatively close, the shafts that gears but they with respect to one another may have practically any spatial relationship; they may be nonparallel or parallel and nonintersecting or intersecting. Bevel gear having appropriate capabilities can be made for each of these arrangements of the shafts. by gears, Parallel shafts can be connected with teeth that are parallel to the shaft axes (spur gears) and straight lengthwise or by gears with screw-like, twisted teeth (helical gears). By gears, Intersecting shafts are connected with tapered teeth arranged on truncated cones (bevel gears). by a gear and worm, nonintersecting or nonparallel shafts are connected usually. Of a long nut that has been bent around a cylinder, the worm resembles the gear and a screw resembles a quarter section.