18"w X 24"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - Brown [Outer Dimensions 19.75"w x 25.75"h] Aluminum Bar + Product Details Size - RG1620AL Quality Packaging carefully packaged 8 Feet Long

+ Product Details Size - 12" X 12" is the size for the duct opening measurement only

+ Product Details Size - 25"w X 28"h is the size for the duct opening measurement only

and 4-way configurations

+ Product Details Size - 16"w X 34"h is the size for the duct opening measurement only

18"w X 24"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace Weather Resistant Air Grille with Screen Mesh Brown [Outer Dimensions 19.75"w x 25.75"h] Aluminum Bar + Product Details Size RG1620AL Quality Packaging carefully packaged 8 Feet Long + Product Details Size 12" X 12" is the size for the duct opening measurement only + Product Details Size 25"w X 28"h is the size for the duct opening measurement only