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 12", Thickness 60 mil (1.5 mm), rounded corners, Brushed Black Finish. Please measure your vent face before ordering Extra Magnetic Strength: Crafted from premium materials, these covers have 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 HVAC systems, AC units, heater vents, and more - Perfect for homes, basements, RVs, and noise reduction in apartment buildings