8" x 28" or 28" x 8" Cube Core Eggcrate Return Air Grille 10in diameter + Product Details Perfect Fit 4 X 12 Is CRFG2028 Width_14in

+ Product Details Perfect Fit & Easy Sizing - Designed for a 18" x 26" OR 26" x 18" duct opening (measured at the opening)

+ Product Details Perfect Fit & Easy Sizing - Designed for a 12" x 18" or 18" x 12" duct opening (measured at the opening)

actual front end outer dimensions are 19

Actual Filter Size – 27 3/4"w x 35 3/4" x 1"

+ Product Details Perfect Fit & Easy Sizing - Designed for a 12" x 24" or 24" x 12" duct opening (measured at the opening)

8" x 28" or 28" x 8" Cube Core Eggcrate Return Air Grille 10in diameter + Product Details Perfect Fit 4 X 12 Is CRFG2028 Width_14in + Product Details Perfect Fit & Easy Sizing Designed for a 18" x 26" OR 26" x 18" duct opening (measured at the opening) + Product Details Perfect Fit & Easy Sizing Designed for a 12" x 18" or 18" x 12" duct opening (measured at the opening)