Lymance Dampers mount easily atop a flue tile with included silicone sealant. The included 32ft stainless cable drops down the flue and mounts in the firebox. The Power Lever is an important feature of this product. A firm tug on the cable drives a piston upward applying a whopping 143 pounds of leverage so the damper always opens easily. Instructions hardware and silicone sealant are included. Size 17in x 17in fits inside flue sizes 15in x 15in to 17.5in x 17.5in.