IMPORTANT! - For STEEL Vents Only: Not suitable for use with aluminum or plastic vents. Please test with a small magnet before ordering IMPORTANT! - Cover Size: 5.5" x 13.75", 60 mil (1.5 mm) thickness, rounded corners. Please measure your vent face before ordering. For other sizes, refer to listing image 6 for SIZE CHART details. Can be trimmed to your desired size easily Extra Magnetic Strength: Crafted from premium materials, our covers provide a surface magnetic strength of up to 650 Gauss, ensuring a complete seal with no slipping - setting us apart from competitors Airflow Control: Effectively blocks hot or cool airflow in unoccupied rooms, enhancing comfort while directing air where it's needed Versatile Use: Ideal for home, HVAC, AC, RV, and heater vents. Perfect for basements, furnace vents, and reducing noise in apartment buildings