Roof Curb For Fan Base Size 42 in Curb Height 12 in Curb Inside Width 37 1/2 in Curb Outside Width 40 1/2 in Material Steel Standards UL 705 For Use With 42 in Square Base Adjustability Fixed Ventilation Type Nonventilated Application General Exhaust Curb Inside Length 37.5 Curb Outside Length 40 1/2 in Curb Shape Square Damper Tray Size 35 in x 35 in Features Flashing Flange One Welded Corner Wood Nailer Finish Galvanized Flashing Flange Width 2 in