Don't buy at all. I don't know for what kind of rack you can use them but I have a 42u at home and I bought a 6u and the 8u on this site and it don't work at all. You can't secure them at all. I have to put tap metal screw or will drill a hole and put a nut and hex screw

Should not be called a “universal” rack tray. Did not fit in either of the racks that I attempted to use them in.

Universal in the sense that this will universally be incompatible with most racks. It has no mounting ears in the front and the only conceivable way to mount this in a rack would be if your rack has middle rails. As it is, it makes a decent floor for my rack I guess. Pretty disappointed though.