17.75 In.H-W 3.7 In.L Squ Gravity Fire Dampr, Damper Application Fire, Frame Material Galvanized Steel, Number of Panels 1, Maximum Air Velocity None, Overall Height 13 3/4 in, Rough Opening Diameter Not Applicable, Rough Opening Shape Square, Fits Fan Diameter Not Applicable, For Duct Shape Square, Free Area 1.7 sq ft, Overall Width 17 3/4 in, Frame Material Thickness 22 ga, Overall Length 3 3/4 in, Connection Type Not Applicable, Frame Depth 3 3/4 in, Rough Opening Length Not Applicable