18" x 26" or 26" x 18" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Compatible With Duct 12in + Product Details Size -

+ Product Details Size - 16"w X 24"h is the size for the duct opening measurement only

easy unrestricted airflow

+ Product Details Size – 10"w X 36"h is the size for the duct opening measurement only

With a 8" diameter for the duct opening measurement

18" x 26" or 26" x 18" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Compatible With Duct 12in + Product Details Size -+ Product Details Perfect Fit & Easy Sizing Designed for a 18" x 26" OR 26" x 18" duct opening (measured at the opening), with actual outer dimensions of 20. 5" W x 28. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 17. 75" x 27. 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