16" X 16" Steel Return Air Filter Grille for 1" Filter - Removable Frame - [Outer Dimensions: 18 5/8" X 18 5/8"] w16h16 you can attain the diameter

you can attain the diameter of the vent

4" X 10" Is The Size For The Duct Opening (floor/vent hole) Measurement Only

4" X 10" Brass Victorian Floor Register Grille - Modern Contempo Decorative Grate - HVAC Vent Duct Cover - Brass Plated

+ Product Details Size - 36"w X 8"h is the size for the duct opening measurement only

16" X 16" Steel Return Air Filter Grille for 1" Filter - Removable Frame - [Outer Dimensions: 18 5/8" X 18 5/8"] w16h16 you can attain the diameter+ Product Details Size 16"w X 16"h is the size for the duct opening measurement only, actual front end outer dimensions are approximately 18 5 8" width X 18 5 8" height Actual Filter Size 15 3 4"w x 15 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.