My hat is off to the trade sheet metal workers. I have learned much from the few I have had the privledge to work with over the years. I am also a tradesman and know that the majority of true knowledge lay on the shop floor with the tradesman and the tools and materials in his/her hands. When working in facilities repair and power plants I too never saw 19 gage.
I am also a retired engineer with cross disipline training. Today I teach welding and order sheet metal often for repairs and projects. I have never been able to purchase 19 gage sheet metal, I usually buy 18g for patch panels. I also salvage large auto panels from donated vehicles or ones I get from the local salvage yard before they are crushed. On the shelves I usually have 10, 12, 16, 18 and 28 gage.
However, never under estimate the automotive industries ability to save a buck or two and get what they want due to bulk purchasing. I have auto/truck sheet metal in the shop from a 38, 50, 63, 64, 85 and 91. Most of it would measure 19 gage (.0418in) 18 gage is about .006 thicker and 20 is about .006 thinner. Students measure it often to determine welding currents. Panels will also vary in thickness due to the die forming and stamping processes. Rust removal or metal work will also stretch or shrink metal. Metal from some of the newest cars is getting thinner and alloyed to make it high strength and corrosion resistant.... and harder to weld.
I also looked at several generations of the Machinery's Handbooks that I collect and they list sheet metal gage from 15/0 to 52 odds and evens in several different standards. One thing I had to get used to when moving from industry to industry is that what is accepted as gospel in one may be a lot different in another. My current industry has lots of varying standards- AWS, SAE, ASME, API, ISO, Asian, European and a host of others. What you find as old hat in one sometimes the others have never heard of!
