6" x 60" Type B Gas Vent Flex Pipe 6GV60F 6" x 60" Type B Gas Vent Flex Pipe is used for offsets when relining a masonry chimney with DuraVent Type B Gas Vent. Add 5â„8†for OD. Diameter: 6" Length: 60" Outer diameter: 6 5/8" .010†Double-wall aluminum flex inner wall (two-ply .005â€) .018†galvalume outer wall with twist-lock connections.