4 in Duct Backdraft Damper Flap
A print-in-place gravity backdraft damper that drops into a 4 in (101.6 mm) round bath-fan duct: a 100.6 mm OD sleeve with a 94.4 mm hinged flap that the fan blows open and gravity swings shut against seven moulded stops, replacing the snapped or missing flap in an old exhaust fan. The 114 mm flange butts the duct end and carries three 3.4 mm holes for M3 / #6 sheet-metal screws; the hinge runs on integral 4 mm pins in 5 mm sockets, printed in one piece with 0.5 mm clearances.
bathroom bath-fan duct damper