I made a connector (female as opposed to your male) for an old radio by
slitting brass tube. Hacksaw and vice produced good enough accuracy for an
excellent operational performance.

How about making a square fixture to hold the round part with two slits
to guide the saw blade?

I have found that a good fret/jewelers saw very handy for cutting small
items. I find it very difficult to cut 1/8 drill rod with a hacksaw
but easy with a fret saw. They cut faster than you expect.