18" X 8" Steel Return Air Filter Grille for 1" Filter - Removable Frame - [Outer Dimensions: 20 5/8" X 10 5/8"] w10h10 + Product Details Size - 4 X 12 Is CRFG2028 Width_14in

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

actual front end outer dimensions are approximately 10 5/8" width X 12 5/8" height

+ Product Details Size - 40"w X 20"h is the size for the duct opening measurement only

actual front end outer dimensions are approximately 34 5/8" width X 28 5/8" height

Designed for optimal air flow and lasting durability

18" X 8" Steel Return Air Filter Grille for 1" Filter Removable Frame [Outer Dimensions: 20 5 8" X 10 5 8"] w10h10 + Product Details Size 4 X 12 Is CRFG2028 Width_14in + Product Details Size 6"w X 6"h is the size for the duct opening measurement only actual front end outer dimensions are approximately 10 5 8" width X 12 5 8" height