Rack and pinions are used for lifting mechanisms (vertical movement), horizontal movement, positioning mechanisms, stoppers and to permit the synchronous rotation of several shafts generally industrial machinery. However, also, they are found in steering systems to improve the direction of cars. The features of rack and pinion systems in steering are as follows: simple framework, high rigidity, small and lightweight, and excellent responsiveness. With this mechanism, the pinion, mounted to the steering shaft, is definitely meshed 
with a steering rack to transmit rotary movement laterlly (transforming it to linear movement) to ensure 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 element to transfer rotary into linear movement, gear racks are often compared to ball screws. There are advantages and disadvantages for using racks instead of ball screws. The benefits of a equipment rack are its mechanical simplicity, huge load carrying capacity, and no limit to the distance, etc. One drawback though may be the backlash. The advantages of a ball screw are the high precision and lower backlash while its shortcomings are the limit in duration due to deflection.
There are Spur Gear Rack applications where the gear rack is stationary, while the pinion traverses and others where the pinion rotates on a fixed axis as the gear rack moves. The previous is used broadly in conveying systems as 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 stock. If the application takes a long duration requiring multiple gear racks in series, we have racks with the tooth forms correctly configured at the ends. These are described as “equipment racks with machined ends”. When a gear rack is produced, the tooth cutting process and heat treatment process could cause it to try & go out of true. We can control this with particular presses & remedial processes.