4-D x 36"l, pellet vent pipe, fully unitized, twist lock construction, can be used in both vertical & horizontal installations, 4-1/2" od, designed for stoves that burn wood pellets, double wall & air insulated pipe, inner wall of 012" super ferritic stainless steel, outer wall 018" laser welded galvalume, patent pending venting for stoves & inserts that use wood pellets, UL listed for 3" clearance to combustibles in USA & Canada, required for venting pellet appliance above 4,000'.