Dura-Vent 3PVP-WS PelletVent Pro Wall Strap with 3 Inside Diameter Laser-welded, double-wall pipe with a .012" inner wall of 444 Stainless steel Outer wall of .018" laser welded Galvalume Encapsulated O-ring gives secondary seal to system. 1" clearance to combustibles in the US and Canada. Stabilizes system with 1" space from wall.