Were talking 1/8th" thick material,,,diameter of pipe goes by inside diameter,,,,until it gets to 10" or larger then it`s measured by outside diameter...theres;10",,12",,16",,20"no half size..sch.40 pipe is 1/4"thick,sch.80 is1/2" thick and so on...i`ve seen sch.20 but then were talking duct...