The Broan® WVK2A Wall Cap Kit is an easy-to-install vent for exhaust fans (bathroom, 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 a padded, weighted back draft damper that prevents outside air from entering the home, and guards ductwork from wind and birds. This kit includes all materials needed for installation, including 5 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.