The rack can be thought of as a gear part with infinite radius, or more simply, it is a straight rod with gear teeth.

Rack and pinion gear systems do not offer as much mechanical power as other systems, but they close this gap by providing more feedback. For example, using a rack and pinion system on a car's steering column will provide better steering feel.
As a mechanical element that transfers rotation to linear motion, gear racks are often compared to ball screws. There are pros and cons to using racks instead of ball screws. The advantages of the gear rack are its mechanical simplicity, large load carrying capacity and no length limitation.
Rack is one of the types of gears commonly used in industry. Racks are used to convert circular motion into linear motion. The rack converts the movement of the rotary pinion gear into single-direction movement, thanks to its teeth opening onto a flat surface.
There are two types of racks called helical and flat racks.