16" X 18" Steel Return Air Filter Grille for 1" Filter - Removable Frame - [Outer Dimensions: 18 5/8" X 20 5/8"] Supply Grille + Product Details Size –

+ Product Details Size – 12" x 30" or 30" x 12" is the size for the duct opening measurement only

[Outer Dimensions: 18

+ Product Details Size – 8"w X 24"h is the size for the duct opening measurement only

+ Product Details Size - The listed 8" diameter refers specifically to the size of the duct opening

How To Measure A Grille

16" X 18" Steel Return Air Filter Grille for 1" Filter - Removable Frame - [Outer Dimensions: 18 5/8" X 20 5/8"] Supply Grille + Product Details Size –+ Product Details Size 16"w X 18"h is the size for the duct opening measurement only, actual front end outer dimensions are approximately 18 5 8" width X 20 5 8" height Actual Filter Size 15 3 4"w x 17 3 4" x 1" High Quality High quality solid stamped steel with counter sunk screw holes (screws included) and no sharp edges Installation Location Sidewall and ceiling Design Removable door face for easy filter change & cleaning uses a 1" thick filter.