American Chimney Supplies Class “A” cap is a great alternative for a Class “A” Chimney System with solid pack insulation. the ACS Class “A” is made of 24 gauge 304 stainless steel. Fore lifetime use with removable lid for future cleanings. Stock diameters 5″ – 12″, Custom diameter made to order same day shipping. Also available in air-cooled style for double & triple walled Class “A”.