The 0800 Series is offered in two frame types to be used with steel duct: a double flange screw hole mounting type (M1) or even a knock-above tab form (M2). The two styles include a simple set up Slash-out template that makes the oval form openings excess easy to Slash. https://jasperfxodr.livebloggs.com/43565379/the-definitive-guide-to-heavy-duty-stainless-steel-damper-manufacturers