12" x 18" Mill Flush Type Louver, 15" x 21" Overall Size, Ventilates 188 SQFT, Heavy Duty Aluminum Construction, 1-1/2" Wide Mounting Flange, 8" x 8" Attached Screen For Insect Protection, Built In Weather Protection, Used For Exhaust Attic Ventilation, Must Be Accompanied By Intake Vents. (Sold in 6-Pk).