M G Duravent 6DVL-66TA 6 Inch Dura-Vent DVL Adjustable 40 Inch -68 Inch Double-Wall Black Pipe has been filling the supply and accessory needs of over 8, 000 sweeps hearth retailers masons and contractors for over 25 years. has the privilege of serving over 80% of the professionals in America.Founded by Robert Daniels Sooty Bob in 1978 has grown from a one-man operation to a national network of six warehouses and a manufacturing plant. From its headquarters in Fairfield Iowa plays a major role in providing for the industry. The telescoping lengths are great for one piece installations from the stove to Dura-Vent Dura/Plus or DuraTech using a Close Clearance Adaptor. The shorter length allows adjustments from 29 - 48 . The longer length gives you 40 - 60 of adjustment. Both pieces must have a minimum of 1 overlap with all connecting pipe. When you are installing Dura-Vent and need reduced clearances on the stovepipe, use DVL. It reduces clearances from combustibles to the stove-pipe from 18 down to 6 for walls and 8 for ceilings. It has an inner wall of .016, 430-alloy stainless steel and an outer wall of .018 aluminized steel painted black. Connecting pipe sections together is easy with predrilled holes and a pack of screws, included. When calculating fit, the outside diameter is 1.125 inches larger than inside diameter. Pipe pieces have a 0.75 inch overlap connection, reducing the usable length by 0.75 inch.