4" BLACK Plastic Round Rotaire Grille Heat Covered Screws Outlet Vent 3940BK RV Trailer Two piece snap together design covers the 2 screw heads. 360 rotation, easy installation and long term durability. Accepts 4" flex duct. See tape measure pictures. Approximate size: Grille face diameter 5 1/2" Back diameter 4" Side: 2" Please let me know if you have any questions. Thank you, Babette |