36" x 8" Cube Core Eggcrate Return Air Filter Grille for 1" Filter w18h18 See chart below:

See chart below:

+ Product Details Size – 16"w X 25"h is the size for the duct opening measurement only

+ Product Details Size - 12"w X 6"h is the size for the duct opening measurement only

10" Diameter Is The Size For The Duct Opening Measurement Only

+ Product Details Size - 18"w X 22"h is the size for the duct opening measurement only

36" x 8" Cube Core Eggcrate Return Air Filter Grille for 1" Filter w18h18 See chart below:+ Product Details Perfect Fit & Easy Sizing Designed for a 36" x 8" OR 8" x 36" duct opening (measured at the opening), with actual outer dimensions of 38. 5" W x 10. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 35. 75" x 7. 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