21.0 Cu. In. 3.5" dia. round fixture support box for use with nonmetallic sheathed cable - Machine tapped fixture holes - New work residential construction 2 HR fire resistive walls and ceilings (50 lbs. fixture support) -Polycarbonate - thermoplastic box with galvanized adjustable stabilizer bar - Size: Depth=2 13/16", Dia=3 1/2" - Mount with Adjustable bar hanger - 16" to 24" on center joist application