Arlington extra heavy duty, plated steel fan fixture box now has higher weight ratings - 150 lb for fixtures and 70 lb for fans when installed on joists spaced 16 in on-center, 70 lb for either a fan or fixture on joists spaced 24 in on-center. Our FBRS4200R features a fully adjustable bracket for installations between joists or rafters spaced from 16 to 24 in on-center. Bracket ends bite into the wood rafter or joist, holding the fan or fixture securely in place.