18" X 18" Steel Return Air Filter Grille for 1" Filter - Removable Frame - [Outer Dimensions: 20 5/8" X 20 5/8"] w36h36 Each grille is securely shrink-wrapped

Each grille is securely shrink-wrapped with a cardboard backing to prevent damage during shipment

Adjustable airflow control - by rotating the middle disk

+ Product Details Size - The listed 4" diameter refers specifically to the size of the duct opening

+ Product Description When it's time to upgrade your HVAC Vents in your house

18" X 18" Steel Return Air Filter Grille for 1" Filter - Removable Frame - [Outer Dimensions: 20 5/8" X 20 5/8"] w36h36 Each grille is securely shrink-wrapped+ Product Details Size 18"w X 18"h is the size for the duct opening measurement only, actual front end outer dimensions are approximately 20 5 8" width X 20 5 8" height Actual Filter Size 17 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.