18 in Backdraft Damper / Wall Shutter, 18-1/2 in x 18-1/2 in, DAYTON, Mfr# 1C744

21 In.H-W 5.75 In.L Alu Wall Backdraft Dampr, Damper Application Backdraft, For Nominal Duct Diameter Not Applicable, Frame Material Galvanized Steel, Number of Panels 1, Maximum Air Velocity 2500 fpm, Overall Height 21 in, Rough Opening Diameter 18 1/2 in, Rough Opening Shape Square, Fits Fan Diameter 18 in, For Duct Shape Not Applicable, Free Area 2 sq ft, Overall Width 21 in, Frame Material Thickness 20 ga, Overall Length 5 3/4 in, Connection Type Not Applicable, Frame Depth 2 1/2 in