4" octagonal box 2-1/8 inches depth 21 cubic inches volume. Concentric knockouts. Wraparound bracket for 2-1/2 inches and 3-5/8 inches steel studs. With integral support bracket. Raised ground screw. Volta VMB-30200

VMB-30200 - Deep Steel Stud Octagonal Box With Knockout (54171-KSSX)