The Gator Cases G-SHOCK-4L 4U Shock Audio Rack with Rubber Shock Suspension is a high-density military grade lightweight polyethylene case with 4U rack space. There are independent rubber double shock absorbers at each corner and 360deg. air ventilation around equipment. An adjustable interior sliding support on each side of rack adjusts front to back as well as up and down for rear support of delicate or heavy gear. The case has threaded field replaceable 7.0mm zinc plated steel rack rails. It also has locking lids, heavy-duty twist latches and comfortable recessed side handles.