Before I developed an interest in blacksmithing I frequently drove past a fabrication shop and occasionally noticed the sign which said “No pipe!” In those days I didn’t understand the significance of the message. Today I can imagine the conversations which prompted the posting.
When I started putting together my shop I made frequent trips to a local scrapyard where I was allowed to wander about and pick out pieces of metal. Looking back, that was a lucky opportunity no longer available nearby. I was able to stock my shop with most of what I would use for several years in round stock, sheet and plate, angle, channel and tool steel.
I also brought home quite a bit of pipe in diameters up to about 3”. Sometime later I learned the distinction between pipe and structural tube. In the subsequent years the pipe has been used in shop building projects or otherwise has been disposed of. It was really round tubing I needed not pipe. I wrote about this once before.
The round tube is available in exact outside diameters in 1/8” increments from 3/8” through 2.5”. That covers almost everything I use. I recently came across the chart of round tubing sizes at this site
I was surprised to see two sizes I hadn’t noticed before - 1-2/3” and 1-9/10”. I know there must be a good reason for offering those dimensions but I have no idea what it is. There is always more to learn.