【Upgrade design】 The 4 inch damper on both sides of the top and bottom of the two new concave inward pressure rib, and increase the thickness to 0.6mm,to ensure that the product is more solid, not easy to damage. 【Material】Hon&Guan 4 backdraft damper and the flap leaves is made of a galvanized steel, the axis are made of aluminum, while the spring are made of carbon steel-2PCS 【Installation method】The position of the 4 inch duct damper spring should be horizontal for horizontal installations so that it can open and close optimally 【Wide applications】Back draught valves can be inserted into havc ducting which are flexible or non-flexible. Designed for use with range hoods, bathroom fans, kitchen and other home HVAC applications 【Lightweight valve wings】The valve wings open under the pressure created by the airflow; when the air flows in the opposite direction, it is automatically closed under the action of the spring, so as to cut off the flow. Rubber ring ensure 100% closure and quiet closing.