18" x 20" or 20" x 18" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Round Damper Ring These are built heavy duty

These are built heavy duty for installation into brick and cement walls

+ Product Details Size - 8"w X 8"h X 2"d (for duct opening measurement only)

+ Product Details Perfect Fit & Easy Sizing - Designed for a 8" x 22" or 22" x 8" duct opening (measured at the opening)

Say goodbye to pest-related worries as the built-in back 1/2" mesh acts as a barrier against unwanted rodents like mice

+ Product Details Size - 28"w X 24"h is the size for the duct opening measurement only

18" x 20" or 20" x 18" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Round Damper Ring These are built heavy duty+ Product Details Perfect Fit & Easy Sizing Designed for a 18" x 20" OR 20" x 18" duct opening (measured at the opening), with actual outer dimensions of 20. 5" W x 22. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 17. 75" x 19. 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