Yes, as John noted, I cut the threads on a lathe, feeding the 60º thread cutting tool bit in one thousandth at a time, until I get close then I switch to 1/2 thousandth. My tool post is set up at 60º also; that is what I feed in by hand (in thousandths). My table feed is set to the thread pitch, and chuck/spindle speed is lowest I can go.
I don't know if anyone makes a Luger barrel thread die or tap. In any event, trying to thread a barrel with a die wouldn't get it concentric with the bore, as John commented.
I have pics of the threading process before & after, but I can't take pics while threading. I need both hands free to throw the appropriate levers to stop the feed and retract the cutting bit at the end of the cut.
"Thread fixer"...Like a thread file? Yes, I have a 20tpi thread file, like for taking dents out of a thread if you were to drop it or something. But if it's serious, like a Luger barrel I had that was soldered to take up gap, then I turn it in the lathe. And/or 'pick up the thread' and re-cut it.