17"W X 10"H [Duct Opening] ALUMINUM RETURN GRILLE - EASY AIR FLOW - LINEAR BAR GRILLES [OUTER DIMENSIONS: 18.875"W X 11.875"H] Compatible With Duct 6in + Product Details Perfect Fit 4 X 12 Is CRFG2028 Width_14in

+ Product Details Perfect Fit & Easy Sizing - Designed for a 16" x 10" OR 10" X 16" duct opening (measured at the opening)

+ Product Details Size – 18" x 36" or 36" x 18" is the size for the duct opening measurement only

Actual Filter Size – 31 3/4"w x 31 3/4" x 1"

With its reliable construction and sleek design

These are airflow control components made to connect to supply grilles of the drop ceiling

17"W X 10"H [Duct Opening] ALUMINUM RETURN GRILLE EASY AIR FLOW LINEAR BAR GRILLES [OUTER DIMENSIONS: 18.875"W X 11.875"H] Compatible With Duct 6in + Product Details Perfect Fit 4 X 12 Is CRFG2028 Width_14in + Product Details Perfect Fit & Easy Sizing Designed for a 16" x 10" OR 10" X 16" duct opening (measured at the opening) + Product Details Size – 18" x 36" or 36" x 18" is the size for the duct opening measurement only