A common feature in IT racks is mounting positions for zero-U accessories, such as power distribution units (PDUs) and vertical cable managers and ducts, that utilize the space between the rear rails and the side of the rack enclosure.OverviewA 19-inch rack is a standardized frame or enclosure for mounting multiple electronic equipment modules. Each module has a front panel that is 19 inches (482.6 mm) wide. The 19 inch dimension includes the edges or e. Equipment designed to be placed in a rack is typically described as rack-mount, rack-mount instrument, a rack-mounted system, a rack-mount chassis, subrack, rack cabinet, rack-mountable, or occasionally simply shelf.