8" Type B Gas Vent 3" - 10" Adjustable Pipe 8GV12A This adjustable pipe is used to add length to a straight length of Type B Gas Vent. 12" adds 3" - 10" of length. Requires a 2" overlap. For Category 1 gas appliances 1" clearance to combustibles Easy-fit twist-lock design with no fitting hassles 0.012" aluminum inner 0.018" galvanized outer .010†Double-wall aluminum flex inner wall (two-ply .005â€) .018†galvalume outer wall with twist-lock connections.