Weatherhood For Blade Diameter 18 in For Cut-Out Height 20 1/2 in For Cut-Out Width 20 1/2 in For Cut-Out Height (With Wall Collar) 23 5/8 in For Cut-Out Width (With Wall Collar) 23 5/8 in Overall Height 22 1/4 in Overall Width 22 1/4 in Overall Depth 18 1/4 in Material Steel Thickness 20 ga Finish Galvanized