6" DuraVent DuraPlus Galvalume Wall Strap 6DP-WS This wall strap is used in interior or exterior installations to support and to stabilize the chimney while assuring a 2" clearance. Wall straps are required every 4' on exterior of building only. Use when air-cooled chimney is required Free-floating inner 430-alloy liner maintains structural integrity in chimney fires 2" clearance to combustibles Outer diameter is 4" larger than inner diameter Triple-wall chimney For uses with wood stoves fireplaces furnaces boilers stoves ranges water heaters or other appliances fueled by wood oil coal or gas Clean smooth exterior finish .016” 430 stainless steel outer wall or .018” galvanized steel outer wall. .018” aluminized steel intermediate liner. .016” 430 stainless steel inner liner. Insulated layers plus ventilated air space. Locks tightly with a precision twist-lock connection.