These rails are popular for use with Dell, IBM, APC, Compaq and HP cabinets/racks. They will fit standard 19", 23" and 30" four post racks, and both depth and width can be adjusted. The full, nested floor allows for weight to be distributed in both the front and back of the shelf. The rails are made from 14 gauge cold rolled steel so they can support at least 110 pounds and are finished with a satin black coating. They occupy 1 RU of rack space. Both 10-32 and 12-24 mounting screw kits are included allowing mount on either thread pattern.