The Gator Cases GR-WH4B1821TB 18U 21" Deep Wall Hanging Hinged Rack is a hinged back double section welded frame rack with 18U rack capacity. The 18 gauge removable panels feature a spring latch. The top and bottom of the rack is 18 gauge cold rolled steel. The perforated top is fan ready and the drilled and tapped front and rear rack rails are 11 gauge with the U numbers printed on them. Remove the rear door for easy installation.