If you have a room full of 2 Post Relay Racks, a bunch of servers, and boxes of 4 Post Rail Kits, then you need to convert your 2 Post Racks into 4 Post Racks by using 2 Post Conversion Kits. The example drawings below illustrates how to convert a 2 Post Rack into one that acts like a 4 Post Rack.
In the example, twenty, 2U, 2 Post Conversion Kits have been stacked on top of one another. The brackets have round holes on one end so that one side might be screwed into the threaded holes of the 2 Post Rack. The the other end of the brackets has square holes. Once the brackets have been mounted to the rack, the square holes will face outward in the front and rear of the rack, essentially now transforming it into a 4 Post. Cage nuts and screws are also included if threaded holes are necessary.