57 In.H-W 12.8 In.L Squ Stl Mtrzd Cntrl Dampr For Nominal Duct Diameter Not Applicable Damper Application Motorized Number of Panels 2 Overall Height 57 in Overall Length 12 3/4 in Rough Opening Shape Square For Duct Shape Square Overall Width 57 in Frame Material Thickness 14 ga Blade Material Galvanized Steel Maximum Air Pressure 4 in wg Overall Diameter 57 in Rough Opening Length 55 in Rough Opening Width 55 in Damper Type Dynamic Maximum Air Velocity 3500 fpm