Features fully unitized, twist-lock construction. Listed at 1” clearance to combustibles in the USA and Canada. It can be used in both vertical and horizontal installations. Stainless steel welded seam inner wall, combined with a galvalume welded seam outer wall. Pipe OD is diameter plus 5⁄8”. Galvalume or painted black outer finish. To calculate installed length, subtract 1 1⁄2” from each length of pipe.