12" DuraVent DuraChimney II Wall Strap 12DCA-WS This wall strap is used to support and to stabilize the chimney in interior or exterior installations to ensure a 2" clearance. Wall straps are required every 8' on exterior of the building only. Approved for wood coal oil and Category 1 gas 430-alloy inner wall 021" galvanized outer Double-wall air cooled chimney system 2" clearance to combustibles Factory-built alternative to pre-fabricated masonry chimneys Lightweight design which eliminates the need for field assembly of pipe sections allowing for faster installation Tested and listed for continuous operation at 1000 ° F flue gas temperatures one hour at 1400 ° F and ten-minutes at 1700 ° F .016†430 stainless steel inner wall and .021†galvanized steel outer wall. For stainless steel outer wall