Use fixed shelves to support equipment without rack-mounted brackets such as modems, CPUs, small power supplies and monitors. Shelves mount to the Universal EIA 5/8"- 5/8"-1/2" (15.9 mm -15.9 mm -12.7 mm) alternating hole pattern of the four vertical mounting rails, and three depths are offered in 18", 24" and 29" (460 mm, 610 mm and 740 mm).