The RVK1A Steel Roof Cap Kit is an easy-to-install vent for ventilation fans (bath, rec room, home gym, etc.). It is compatible with 3" or 4" ductwork and includes a 3" to 4" adapter for convenience. This cap features both a back draft damper and bird screen, preventing outside air from entering the home and birds and small pests from entering duct work. This kit includes all materials needed for installation, including 8 ft. of 4" flexible ducting, 4" metal duct connector, 4" to 3" Reducer, nylon zip ties and mounting screws. The flexible ducting conforms to UL 181 Class 1 Air Connector and CUL S110 requirements. Not suitable for dryer venting or flat roofs. Features: Broan-NuTone Bathroom Exhaust Fans Built-in backdraft damper prevents outside air from entering home Built-in bird screen prevents birds and other small animals from entering duct work Kit includes all materials needed for install: 8 ft. of 4" flexible ducting, 4" metal duct connector, 4" to 3" Reducer, nylon zip ties and mounting screws Constructed of durable, resilient steel with a black powder coat finish Easy to install in new construction, replacement, or DIY applications Compatible with 3" and 4" round ducting Not suitable for dryer venting or flat roofs