Round 7.9 in dia GStl Mtrzd Smoke Damper For Nominal Duct Diameter 8 in Damper Application Smoke Number of Panels 1 Overall Height 7 7/8 in Overall Length 8 1/8 in Rough Opening Shape Round For Duct Shape Round Overall Width 8 1/4 in Frame Material Thickness 20 ga Blade Material Galvanized Steel Maximum Air Pressure 4 in wg Overall Diameter 7 7/8 in Rough Opening Width 8 in Damper Type Dynamic Maximum Air Velocity 3000 fpm Nameplate Voltage 120V AC Rough Opening Diameter 8 in