How to Measure: Always measure the wall opening to determine which size you should order. Wall Opening Size(24"W x 12"H) = Listed Size(24"W x 12"H, Duct Opening). 24"W x 12"H is the size for the duct opening measurement only, actual return air grille outer dimensions are 25.75"W x 13.75"H. ATTENTION: This is a flat return air grill used for mounting on the wall directly (Screws included). High-Quality Materials: Embodying a powder-coated finish, the return air grill exhibits resilience against flaking, scratching, and fading, the cold air return vent cover is made of high-quality steel, and the steel is stamped so there are no sharp edges. Modern vent covers for home ceilings are a sturdy construction that ensures long-term durability, making them a reliable choice for residential and commercial applications.