Roof Curb Adapter, Adapter Type Increaser, For Fan Base Size 33 1/2 in, For Curb Size 40 in, Material Steel, For Fan Type Downblast Fans, Filtered Supply Fans, Upblast Fans, Curb Side Width 40 in, Fan Side Width 33 1/2 in, Finish Galvanized, Function Adapts 34 in Fan Base to Fit 40 in Roof Curb, Includes (12) 1/4-20 Tinnerman Speed Nut, (12) 1/4-20 x 3/4 Bolts, Metal Material Thickness 18 ga, Number of Fasteners per side 3, Overall Height 5 in, Top Flange Height 2 1/2 in