M-Flex™ standard liner kits are used for wood, oil, coal and gas appliances. Each of our 0.006 in (CB) and 0.005 in (CBF) standard kits comes with installation instructions and a lifetime warranty. This lining kit has been installed in venting applications since 1992 and continues to be the most popular all fuels kit we offer. We stock 3 to 8 in ID as well as 6 to 8 in OD in our 0.006 in OD(CB). Kits are the same price as ID kits, just add OD to the part number when ordering. For example: CB625KITOD. NATIONAL™ CHIMNEY M-Flex™ Liner Kit, Standard, 35 ft Length, 5 in Width, Domestic