apart from having the tool exactly on centre height, sharp edges to
the cutting tool, and experimenting with cutting speeds there are no
other tricks to getting polished threads at 7mm x 48tpi are there?
I'd welcome a description of how you get really schmick threads at
this size.

The problem you're fighting is cutting speed. The SFPM on that small a
diameter is too slow unless the lathe is running at high RPM.

Karl