Rack and pinions are used for lifting mechanisms (vertical movement), horizontal movement, positioning mechanisms, stoppers and also to permit the synchronous rotation of many shafts generally industrial machinery. On the other hand, they are also found in steering systems to change the direction of cars. 
The characteristics of rack and pinion systems in steering are the following: simple structure, high rigidity, small and lightweight, and excellent responsiveness. With this mechanism, the pinion, installed to the steering shaft, can be 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 toys and lateral slide gates.
As a mechanical element to transfer rotary into linear motion, gear racks tend to be in comparison to ball screws. There are pros and cons for using racks instead of ball screws. The benefits of a gear rack are its mechanical simplicity, large load carrying capacity, no limit to the distance, etc. One drawback though is the backlash. The benefits of a ball screw are the high precision and lower backlash while its shortcomings include the limit in duration 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 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 stock. If the application requires a long duration requiring multiple equipment racks in Spur Gear Rack series, we’ve racks with the tooth forms properly configured at the ends. They are described as “gear racks with machined ends”. Whenever a equipment rack is created, the tooth cutting process and the heat treatment process could cause it to try & walk out true. We can control this with special presses & remedial processes.