Rack and pinions are used for lifting mechanisms (vertical movement), horizontal movement, positioning mechanisms, stoppers and to let the synchronous rotation of several shafts in general industrial machinery. However, they are also used in steering systems to change the direction of vehicles. The characteristics of rack and pinion systems in steering are the following: simple framework, high rigidity, small and lightweight, and excellent responsiveness. With this system, the pinion, mounted to the steering shaft, is usually meshed with a steering rack to transmit rotary movement laterlly (switching it to linear motion) so that you can control the wheel. In addition, rack and pinions are used for many other purposes, such as playthings and lateral slide gates.
As a mechanical component 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 equipment rack are its mechanical Spur Gear Rack simplicity, large load carrying capacity, and no limit to the distance, etc. One drawback though is the backlash. The benefits of a ball screw will be the high precision and lower backlash while its shortcomings include the limit in size 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 as the gear rack moves. The previous is used widely in conveying systems while 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 requires a long size requiring multiple equipment racks in series, we have racks with the tooth forms properly configured at the ends. They are described as “gear racks with machined ends”. When a gear rack is created, the tooth cutting procedure and heat treatment process could cause it to try & walk out true. We can control this with particular presses & remedial processes.