6" DuraVent DVL Double-Wall 12" Adjustable Black Pipe 6DVL-12ADJ This adjustable pipe is used to add length to DVL pipe. 12" pipe adds 2" - 11" of length. 12" section can be ovalized for oval-to-round appliance connector. Use with DuraVent factory-built chimneys 430-alloy stainless inner wall aluminized steel outer wall 1" outer diameter Reduces clearances from 18" to 6" for walls Reduces clearances from 18" to 8" for ceilings Sturdy construction to ensure long-lasting durability Creates a tight secure connection in your venting system .016” stainless steel inner wall. .018” galvanized outer painted black.