Rack and pinions are used for lifting mechanisms (vertical movement), horizontal motion, positioning mechanisms, stoppers and to let the synchronous rotation of many shafts generally industrial machinery. On the other hand, also, they are used in steering systems to change the direction of cars. The features of rack and pinion systems in steering are as follows: simple structure, high rigidity, little and lightweight, and excellent responsiveness. With this mechanism, the pinion, installed to the steering shaft, is certainly meshed with a steering rack to transmit rotary movement laterlly (switching it to Spur Gear Rack linear motion) so that you can control the wheel. Furthermore, rack and pinions are used for several other purposes, such as toys and lateral slide gates.
As a mechanical component to transfer rotary into linear motion, gear racks tend to be compared 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 space, etc. One drawback though may be the backlash. The advantages of a ball screw will be the high precision and lower backlash 
while its shortcomings include the limit in length due to deflection.
There are applications where the gear rack is stationary, while the pinion traverses and others where in fact the pinion rotates upon a fixed axis as the gear rack moves. The previous is used widely in conveying systems while the latter can be utilized in extrusion systems and lifting/lowering applications.
To provide many variants of rack and pinion, KHK has various kinds of gear racks in share. If the application requires a long length requiring multiple equipment racks in series, we have racks with the tooth forms correctly configured at the ends. They are described as “gear racks with machined ends”. Whenever a gear rack is produced, the tooth cutting procedure and the heat treatment process could cause it to try & go out of true. We are able to control this with particular presses & remedial processes.