The SRK 19" Universal Equipment Racks are available in four sizes to accommodate any rack-mounted equipment setup: 8 (SRK8), 12 (SRK12), 16 (SRK16) and 21 (SRK21). All racks are constructed of heavy-duty steel with fully enclosed side panels and front and rear rack rails. The side panels are also perforated for passive ventilation. The racks are mounted on four 3" (75mm) casters with lockable fronts that can handle a weight capacity of up to 300lb (450lb without casters). Each rack comes with a blank, single-space panel. Finally, their unique steel support bar design allows these racks to be compatible with either U.S. or European thread sizes, with both sets of screws included.