The D4B-FS-R series is designed for non insulated ceilings. A unique design allows installation of very shallow plenums as low as 4" (when used with a shallow cover. A black powder coated 20 Ga. baseplate is designed for bidirectional mounting of hanger bars. A 18 Ga. galvanized steel junction box with multiple K.O. for easy wiring entry. The housing series is approved for branch circuit wiring.