Stops Down Drafting. Wind driven, the slightest breeze provides positive ventilaton with no chance of down drafting. Totally enclosed ball bearing system. No additional maintenance. Please Note: This type of cap only works when the wind blows. It will not solve a smoking problem cause by negative air pressure of a poor drafting chimney. Will fit into a 10" round metal or masonry chimney. Can be adapted to a square or retangular massony chimney with our adaptor plate. Made in the USA. Availability: Usually ships the same business day. 30010TBCRegular price: $289.95Sale price: Copyright © 2008 Chimney Depot Inc. All rights reserved.