This DuraTech chimney flue pipe measures 36" length, and is available with a 5" or 6" inside diameter. It's built with 430 alloy stainless steel inner wall, and stainless outer walls. The ThermaTech blanket insulation eliminates hot spots, with no shifting, settling, or voids. It features twist-lock design for safe and easy connection / disconnection without mechanical fasteners. No locking bands are required. Outer diameters are 2" larger than the outer. Allow 2" clearance to combustibles. DuraTech is tested and listed to the UL 103HT Standard for use with wood, oil, coal, and gas appliances in the 5"-8" sizes. Need another size? Call us at 716-442-3004. Limited lifetime warranty.(NOTE: Use the 6" DuraTech chimney pipe for our Chicago Brick Oven kits.) Shipping is FREE in the contiguous US.