The economical Atlas Sound 121-18 cabinet is 22 5/16" wide, 18 1/2" deep, and contains 21RU vertical panel spaces. The 121-18 cabinet includes one pair of 11 ga. CRS fixed mounting rails. The serie is constructed of 16 ga. CRS and include base, top panel, side panels, mounting rails, a removable rear door with cylinder lock and flush door pull handle. Offers several installer-friendly advantages, including an expanded 6RU opening in the cabinet top and bottom which can be left open for wire access and/or ventilation, or closed using a standard vent or solid panels. Rear doors (included with all models) are hung with quick-release spring hinges which allow them to be rotated 180° for right or left-hand opening. If a front door is ordered, it will be keyed differently than the rear door for security. Rack rails are precision tapped 10-32 and recessed 11/16" (17.5mm). These plated rails include convenient RU indicator hash marks to aid in equipment alignment. Rails are standard E.I.A. 5/8"-5/8"-1/2" spacing. Conduit arrays are located on the top and bottom surface panels, as well as the top and bottom back flanges. Flange arrays consist of five knockouts, three 1" (25mm) standard, and two 1/2" (13mm) x 3/4" (19mm) concentric. Surface arrays are comprised of 4 knockouts, two, 1" (25mm) standard knockouts and two 1/2" (13mm) x 3/4" (19mm) concentric. Stamped, perforated vents are located on all sides as well as on the rear door to allow for maximum air convection. Cabinet surfaces are phosphate pre-treated for proper paint adhesion of the textured black epoxy finish.