The Lock-Top Damper has a stainless steel cap attached to a cast aluminum frame by a series of stainless spring cables. It comes with a 30 foot cable that drops down the chimney and is operated by a handle mounted on the firebox. It comes with a Chimney Fire Safety Device that locks the damper open in the event of a chimney fire. It fits indoor chimney sizes from 6 x 9 inches to 9 1/2 inches x 12 1/2 inches and has a cross sectional area of 70 sq. inches.