Our return air filter grilles have horizontal bars are fixed at 45 degrees for great airflow dynamics. Each product features concealed hinges and latches to achieve a clean and modern look. R6 Fiberglass Back Plenum accepts 6" to 18" Round Spin-in Collars or Start Collars (not included) - Accepts 1" disposable filter (not included) - Recommended Size: 20x20x1. Each grille is carefully shrink wrapped with cardboard backing to prevent damage in shipment.