Most rigid chimney liner sections are made of nonmagnetic, series 304L or series 316L stainless steel. Unlike the flexible stainless steel liner, rigid pipe comes in sections and is usually round in shape and one to four feet long and five to ten inches or more in diameter. The most common wall thickness is 24-guage (0.024 in.) or 22-guage (0.029 in.) stainless steel.
304L is for venting wood appliances. 316L is for venting wood, coal, oil, and gas burning appliances.