8" x 12" or 12" x 8" Cube Core Eggcrate Return Air Filter Grille for 1" Filter - Aluminum - White [Outer Dimensions: 10.5" X 14.5"] w36h36 + Product Details Size -

+ Product Details Size - The listed 12" diameter refers specifically to the size of the duct opening

and the included installation screws make setup simple and efficient

+ Product Details Size – 20" x 36" or 36" x 20" is the size for the duct opening measurement only

with no sharp edges

actual front end outer dimensions are approximately 10 5/8" width X 20 5/8" height

8" x 12" or 12" x 8" Cube Core Eggcrate Return Air Filter Grille for 1" Filter - Aluminum - White [Outer Dimensions: 10.5" X 14.5"] w36h36 + Product Details Size -+ Product Details Perfect Fit & Easy Sizing Designed for a 8" x 12" or 12" x 8" duct opening (measured at the opening), with actual outer dimensions of 10. 5" W x 14. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 7. 75" x 11. 75" x 1" Premium Airflow Efficiency High performance cube core eggcrate design allows 95% airflow efficiency, reducing energy costs and maximizing HVAC system lifespan. Durable, Rust Free Aluminum