Roof Curb, For Fan Base Size 16 in to 21 1/2 in, Curb Height 12 in, Curb Inside Width 10 1/2 in to 19 in, Curb Outside Width 14 1/2 in to 23 in, Material Steel, Standards UL 705, For Use With 16 in to 21 1/2 in Square Base, Adjustability Adjustable, Ventilation Type Nonventilated, Application General Exhaust, Curb Shape Square, Damper Tray Size 12 in to 19 in, Features Flashing Flange, Finish Galvanized, Flashing Flange Width 4 in, For Fan Type Downblast Fans, Filtered Supply Fans, Upblast Fans