Electrical Box Box Type Square Number of Gangs 2 Bracket Type FM Capacity 21 cu in Material Galvanized Steel Number of 1/2 in Back Knockouts 1 Number of 1/2 in Side Knockouts 3 Clamp Type NM-B Number of 3/4 in Side Knockouts 1 Nominal Depth 1 1/2 in Nominal Length 4 in Nominal Width 4 in Color Silver Standards UL