16" x 18" or 18" x 16" Cube Core Eggcrate Return Air Grille Copper Coil-Insulated Line Set + Product Details Perfect Fit 4 X 12 Is CRFG2028 Width_14in

+ Product Details Perfect Fit & Easy Sizing - Designed for a 8" x 30" or 30" x 8" duct opening (measured at the opening)

+ Product Details Perfect Fit & Easy Sizing - Designed for a 24" x 30" OR 30" x 24" duct opening (measured at the opening)

+ Product Spec Sheet Aluminum Return Grille Spec Sheet

Actual Filter Size – 31 3/4"w x 29 3/4" x 1"

+ Product Details Size – 6" x 36" or 36" x 6" is the size for the duct opening measurement only

16" x 18" or 18" x 16" Cube Core Eggcrate Return Air Grille Copper Coil Insulated Line Set + Product Details Perfect Fit 4 X 12 Is CRFG2028 Width_14in + Product Details Perfect Fit & Easy Sizing Designed for a 8" x 30" or 30" x 8" duct opening (measured at the opening) + Product Details Perfect Fit & Easy Sizing Designed for a 24" x 30" OR 30" x 24" duct opening (measured at the opening)