6"W X 16"H [Duct Opening] Steel Air Vent Return Grille - HVAC VENT DUCT COVER DIFFUSER - [Outer Dimensions: 7.75"W X 17.75"H] Material_Steel actual front end outer dimensions 4" Round Duct Pipe Product Details Size The SHEASC10W1-HP

actual front end outer dimensions are approximately 38 5/8" width X 22 5/8" height -

+ Product Details Size – 16"w X 18"h is the size for the duct opening measurement only

+ Product Details Perfect Fit & Easy Sizing - Designed for a 36" x 20" OR 20" x 36" duct opening (measured at the opening)

But for plumbing it will fit onto a pipe that is 1/4" on the "inside" (ID) which equals to 1/2 on the outside

+ Product Details Perfect Fit & Easy Sizing - Designed for a 20" x 36" OR 36" x 20" duct opening (measured at the opening)

6"W X 16"H [Duct Opening] Steel Air Vent Return Grille HVAC VENT DUCT COVER DIFFUSER [Outer Dimensions: 7.75"W X 17.75"H] Material_Steel actual front end outer dimensions 4" Round Duct Pipe Product Details Size The SHEASC10W1 HP actual front end outer dimensions are approximately 38 5 8" width X 22 5 8" height + Product Details Size – 16"w X 18"h is the size for the duct opening measurement only