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 12" 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 3012TBCRegular price: $359.95Sale price: Copyright © 2012 Chimney Depot Inc. All rights reserved. Call Us @ 1-702-483-1587