8"w X 6"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 9.75"w x 7.75"h] Compatible With Duct 6in + Product Details Perfect Fit 4 X 12 Is CRFG2028 Width_14in

+ Product Details Perfect Fit & Easy Sizing - Designed for a 26" x 18" OR 18" x 26" duct opening (measured at the opening)

+ Product Details Size - 16"w X 36"h is the size for the duct opening measurement only

+ Product Details Size - 20"w X 24"h X 2"d (for duct opening measurement only)

actual front end outer dimensions are approximately 36 5/8" width X 24 5/8" height

75" Width X 17

8"w X 6"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace Weather Resistant Air Grille with Screen Mesh [Outer Dimensions 9.75"w x 7.75"h] Compatible With Duct 6in + Product Details Perfect Fit 4 X 12 Is CRFG2028 Width_14in + Product Details Perfect Fit & Easy Sizing Designed for a 26" x 18" OR 18" x 26" duct opening (measured at the opening) + Product Details Size 16"w X 36"h is the size for the duct opening measurement only