8"w X 36"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 9.75"w x 37.75"h] steel + Product Details Size -

+ Product Details Size - 40"w X 6"h is the size for the duct opening measurement only

8" Diameter Is The Size For The Duct Opening Measurement Only

Filter Size - 35

Actual Filter Size – 31 3/4"w x 23 3/4" x 1"

+ Product Description Introducing HVAC Premium's Aluminum Adjustable Return Grill – the key to enhanced air control and energy efficiency

8"w X 36"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 9.75"w x 37.75"h] steel + Product Details Size -+ Product Details Size 8"w X 36"h X 2"d (for duct opening measurement only); actual front end outer dimensions are 9. 75" Width X 37. 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 wear