7" Cape back draft damper,made by Tamarack Technologies. Very clever design, uses a special fabric that opens when exhaust fan is turned on and then collapses when fan is off. Like new, used very briefly in our cabin. This 7" model slides into standard 7" ducting, so you don't have to cut or join ducting together, just slide it in at the exterior end.
Their price is $25 plus tax and shipping. I will sell this one for $20 cash, firm.
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