Grinding a small Internal Trapezoidal threading tool

[TomG]

It depends on the shape of the nut. I've squeezed things like that with a three jaw, or if that won't do it you may have to make a die that you can use in your mill vise. Anything that compresses the nut evenly will do.

For a tap, I would make it out of O1 so you can do all the machining. O1 should be hard enough to cut brass as is, or you can harden it with an oil quench.

Tom