Chicago plenum, 2-1/8" deep, 4" square drawn boxes with (8) 1/2" & (4) 3/4" side knockouts and (2) 1/2" & (2) 3/4" bottom knockouts are installed in air plenum walls or ceilings for lighting fixtures, switches, receptacles or other outlet devices. 1/4” threaded rod couplings are welded to the back of boxes for a quick mounting on threaded rods. Cut the rod to desired length and spin box on, in one easy step. Square boxes are used to bring power to a number of electrical devices where multiple conductor runs are split in two or more directions. Garvin Industries’ 4S Boxes can be surface- or flush mounted when multi directional conduit runs are necessary. Red painted boxes are also available to easily distinguish fire alarm circuits.