My welding table uses round pipe and has clamps to take care of the
slop. The clamps are holes in the outer pipe with a nut welded to add
threads. And then a bolt with a bar welded to it to make it into a
wing bolt. With square tubing you will either need two clamps or put
the hole on the corner so it locks in two directions.

The last wing bolt I made was done with silver solder. I ground and
filed a groove in the head that fitted the rod and gave the silver
solder a fairly large area of close contact.. Silver solder would work
well in securing a nut to the flat side of square tubing. I did have
to use two propane hand torches to get enough heat. Might have be able
to use just one and some insulating firebrick to capture the heat.


Dan