18 In.dia SS Barometric Draft Control Damper Application Barometric Draft Control For Nominal Duct Diameter 17 in 18 in Frame Material Steel Number of Panels Not Applicable Maximum Air Velocity Not Applicable Overall Height 19 1/2 in Rough Opening Diameter 18 in Rough Opening Shape Round Fits Fan Diameter Not Applicable For Duct Shape Round Free Area Not Applicable Overall Width 19 1/2 in Frame Material Thickness 18 ga Overall Length 24 5/8 in Connection Type Press Fit