NuTone WVK2A Flexible Wall Ducting Kit for Ventilation Fans, 4-Inch White wall cap for 4 round duct - includes 4 mounting screws Engineered resin material for impact and UV resistance Weighted hood guards against wind, birds or lint build-up 3 to 4 duct adapter 5 of 4 diameter flexible foil ducting conforms to UL 181 Class 1 Air Connector requirements