ed wrote::roll: Wall thickness of tube steel conversion 13bwg to inches
bwg stands for Birmingham Wire Gauge. A reference I found at
http://www.unc.edu/~rowlett/units/scales/wiregauge.html "How Many? A Dictionary of Units of Measurement" (© Russ Rowlett and the University of North Carolina at Chapel Hill) shows that 13 bwg is 0.095 inches.