6" X 36" DuraVent DuraLiner Oval Rigid Pipe 6DLR-36O 6" X 36" DuraLiner Oval Rigid Pipe is used to reline masonry chimneys with 0/0 clearance. Factory-insulated. Built-in pre-drilled fittings for riveting joints. 304 stainless steel inner and aluminized steel outer. Diameter: 6" Length: 36" 304 stainless steel inner and aluminized steel outer Factory-insulated. Built-in pre-drilled fittings for riveting joints .016†304 stainless steel inner liner. Rigid relining pipe: double-walled with 304 stainless steel inner and galvalume outer. Factory insulated between inner and outer walls.