6"w X 18"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 7.75"w x 19.75"h] Color_Red Oak Actual Filter Size – 21

Actual Filter Size – 21 3/4"w x 11 3/4" x 1"

but still very thin

+ Product Details Perfect Fit & Easy Sizing - Designed for a 32" x 12" OR 12" x 32" duct opening (measured at the opening)

+ Product Details Size - 16"w X 10"h is the size for the duct opening measurement only

+ Product Details Size - 24"w X 16"h is the size for the duct opening measurement only

6"w X 18"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 7.75"w x 19.75"h] Color_Red Oak Actual Filter Size – 21+ Product Details Size 6"w X 18"h X 2"d (for duct opening measurement only); actual front end outer dimensions are 7. 75" Width X 19. 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