12"w X 20"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 13.75"w x 21.75"h] Aluminum and the second number represents

and the second number represents the height

75"H – fits a 12" X 8" duct opening

actual front end outer dimensions are approximately 38 5/8" width X 14 5/8" height -

+ Product Details Size - 10"w X 18"h X 2"d (for duct opening measurement only)

12"w X 20"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 13.75"w x 21.75"h] Aluminum and the second number represents+ Product Details Size 12"w X 20"h X 2"d (for duct opening measurement only); actual front end outer dimensions are 13. 75" Width X 21. 75" Height Weather and Pest Proof These louvers are especially designed to prevent water from entering your home, and with a built in back 1 2" mesh they also protect you from annoying rodents like mice, rats, birds, and squirrels High Quality Aluminum The premium durable aluminum will never rust and it will never