Roof Curb For Fan Base Size 42 in Curb Height 18 in Curb Inside Width 37 in Curb Outside Width 40 1/2 in Material Steel Standards NFPA 96 UL 705 UL 762 For Use With NFPA 96 UL 705 UL 762 Adjustability Fixed Ventilation Type Ventilated Application Commercial Kitchen Curb Inside Length 37 Curb Outside Length 40 1/2 in Curb Shape Square Features Flashing Flange Finish Galvanized Flashing Flange Width 4 in For Fan Type Downblast Fans Filtered Supply Fans Upblast Fans