4" X 48" DuraVent Dura-Connect Double-Wall Flex Gas Connector Pipe 4DV48DW This connector pipe is used as a connector system to replace rigid gas vent with a flexible section. DuraConnect II can be used when Type B gas vent double-wall connector is required. Not to be enclosed and cannot penetrate through walls floors or ceilings. Twist-lock connectors on each end. 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 Outer diameter is 5/8" larger than inner diameter .010†aluminum (2-ply of .005â€)