I do this a lot at work. It’s not easy to weld galved steel, so either grind/sand off the zinc on the nut (not the easiest to do if they’re small!) or use a plain steel nut. If the tube is galved, sand the galv off that too around the area of the weld.
The fumes from zinc are toxic so wear a mask and weld in a well ventilated area.
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Nice!