The current Dell Rail Kit design is compatible with both square hole Server Racks as well as round hole Server Racks. This innovative design is the first production Rail Kit that has this unique feature. The ends of the Dell Rail have a rotating assembly that has square hooks on one surface and PEM nuts on the opposite surface. This mechanism is simple and versatile but has the potential to cause an obstruction with some types of Server Racks, specifically ones with C Channel uprights.
If you are having obstruction issues installing Dell Rail Kit there are several products that will fix your problem. RackSolutions makes several different kits that replace the rotating portion of the Dell Rail Kit with a simple bracket that does not cause an obstruction.