Rack and pinions are used for lifting mechanisms (vertical movement), horizontal movement, 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 improve the direction of cars. The features of rack and pinion systems in steering are as follows: simple structure, high rigidity, small and lightweight, and superb responsiveness. With this mechanism, the pinion, installed to the steering shaft, is definitely meshed with a steering rack to transmit rotary 
movement laterlly (switching it to linear movement) 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 element to transfer rotary into linear motion, gear racks tend to be in comparison to ball screws. There are advantages and disadvantages for using racks instead of ball screws. The benefits of a gear rack are its mechanical simplicity, huge load carrying capacity, no limit to the distance, etc. One disadvantage though is 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 broadly in conveying systems while the latter can be used in extrusion systems and lifting/lowering applications.
To provide many variations of rack and pinion, KHK has many types of gear racks in share. If the application requires a long length requiring multiple gear racks in series, we have racks with the tooth forms properly Spur Gear Rack configured at the ends. They are described as “gear racks with machined ends”. When a gear rack is created, the tooth cutting procedure and the heat treatment process can cause it to try & walk out true. We can control this with unique presses & remedial processes.
