10" x 18" or 18" x 10" Cube Core Eggcrate Return Air Grille Grilles + Product Details Size –

+ Product Details Size – 4"w X 10"h is the size for the duct opening measurement only

Measuring 3" in diameter for the duct opening

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

Actual Filter Size – 13 3/4"w x 15 3/4" x 1"

actual front end outer dimensions are 17" Width X 17" Height

10" x 18" or 18" x 10" Cube Core Eggcrate Return Air Grille Grilles + Product Details Size –+ Product Details Size 10" x 18" or 18" x 10" is the size for the duct opening measurement only, actual front end outer dimensions are approximately 11. 75" X 19. 75". High Quality High quality, rust free aluminum construction with smooth finished edges and counter sunk screw holes (screws included); no sharp edges.. Installation Location sidewall and ceiling. Design Cubic core eggcrate design Offers highest airflow efficiency at almost 95%, reducing