Rack and pinions are used for lifting mechanisms (vertical movement), horizontal movement, positioning mechanisms, stoppers and to permit the synchronous rotation of a number of shafts in general industrial machinery. On the other hand, also, they are found in steering systems to change the direction of vehicles. The features of rack and pinion systems in steering are as follows: simple framework, high rigidity, small and lightweight, and exceptional responsiveness. With this mechanism, the pinion, mounted to the steering shaft, is meshed with a steering rack to transmit rotary motion laterlly (converting it to linear motion) so that you can control the wheel. Furthermore, rack and pinions are used for several other purposes, such as playthings and lateral slide gates.
As a mechanical element to transfer rotary into linear movement, gear racks tend to be 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, huge load carrying capacity, and no limit to the distance, etc. One disadvantage though may be the backlash. The advantages of a ball screw will be the high precision and lower backlash while its shortcomings are the limit in size due to deflection.
There are applications where in fact the gear rack is stationary, while the pinion traverses and others 
where the pinion rotates on a fixed axis while the gear rack moves. The former is used widely in conveying systems while the latter can be utilized in extrusion systems and lifting/lowering applications.
To provide many variations of rack and pinion, KHK has various kinds of gear racks in share. If the application takes a long size requiring multiple gear racks in series, we’ve racks with the tooth forms Spur Gear Rack correctly configured at the ends. They are described as “gear racks with machined ends”. When a gear rack is produced, the tooth cutting procedure and heat treatment process can cause it to try & go out of true. We can control this with particular presses & remedial processes.