Do you have a broken, rusted,seized,or worn out original damper and want a cheap better alternative to having it replaced by a mason? The "Lock-Top" or "Lyemance" style dampers are the answer. Better then your original damper because they provide a seal at the top of the chimney stopping more energy loss, all pest infestations, and a chimney's worst enemy... water damage!
**CAUTION: All top mount dampers are not to be used in conjunction with gas logs or gas appliances. In the case of a gas leak, an explosion could occur. **
Lyemance Dampers Lock-Top Dampers Fireplace Dampers
Drop In Dampers Stovepipe Dampers
Discount Chimney Supply Inc. (2011)