Rack and pinions are used for lifting mechanisms (vertical movement), horizontal motion, positioning mechanisms, stoppers and to permit the synchronous rotation of many shafts in general industrial machinery. However, they are also found in steering systems to change the direction of vehicles. The features of rack and pinion systems in steering are the following: simple framework, high rigidity, little and lightweight, and superb responsiveness. With this system, the pinion, mounted to the steering shaft, is usually meshed with a steering rack to transmit rotary motion laterlly (transforming it to linear movement) to ensure that you can control the wheel. In addition, rack and pinions are used for several other purposes, such as playthings and lateral slide gates.
As a mechanical element to Spur Gear Rack transfer rotary into linear movement, gear racks are often in comparison to ball screws. There are pros and cons for using racks instead of ball screws. The advantages of a gear rack are its mechanical simplicity, large load carrying capacity, no limit to the length, etc. One drawback though is the backlash. The benefits of a ball screw will be the high precision and lower backlash while its shortcomings are the limit in duration due to deflection.
There are applications where the gear rack is stationary, as the pinion traverses and others where the pinion rotates on a fixed axis while the gear rack moves. The previous is used broadly in conveying systems as the latter can be used in extrusion systems and lifting/lowering applications.
To provide many variants of rack and pinion, KHK has many 
types of equipment racks in share. If the application takes a long duration requiring multiple gear racks in series, we have racks with the tooth forms properly configured at the ends. They are described as “equipment racks with machined ends”. When a gear rack is created, the tooth cutting procedure and the heat treatment process could cause it to try & walk out true. We can control this with particular presses & remedial processes.