Weatherhood For Blade Diameter 16 in For Cut-Out Height 18 1/2 in For Cut-Out Width 18 1/2 in For Cut-Out Height (With Wall Collar) 21 5/8 in For Cut-Out Width (With Wall Collar) 21 5/8 in Overall Height 20 1/4 in Overall Width 20 1/4 in Overall Depth 17 in Material Steel Thickness 20 ga Finish Galvanized