RACKMOUNT SHELVINGs are generally defined by the U specification 1U is equal to 1.75 inches (1u=1.75inches). 1u, 2u, 3u, 4u, 5u, etc. Special cabinets generally ranging from 10-40U are readily available from standard and custom built computer manufacturer's like SOS2000 COMPUTER SYSTEMS. The most common type of cabinet is known as the "EIA standard" or "19-inch rackmount cabinet", where 19-inch refers to the approximate internal width of the cabinet, from mounting bracket to mounting bracket.