OK, uncle on finding the nut, how can I make the groove
So, I visited some more places today, one of which has a special tubing department. They were great, but ultimately didn't have what I needed.
Now, my thoughts turn to trying to figure out how to make that groove in a piece of 3/8" copper tubing. There must be a tool that does it, but dang if I've found it. Any ideas for jury rigging something for a one-time shot?
As always, your help and cleverness is greatly appreciated.