[Coffee in hand] I'm thinking a joining sleeve
and the splice over a cut, 'turnbuckle' threaded
mixing a right handed thread , and a left handed thread ,
so rotating the splice tube pulls the threaded cut sections together , it self being a matching thread,
with an internal shoulder to match the 2 pieces being joined and having them well aligned
when all 3 butt together will have a raised ring in the center...
Classic 'screwed and glued' AlAn Frames were machined in a similar manner ,
rotating the frame tubes pulled the 'lug' ends together, they being threaded,
while epoxy was still yet to cure.
Violin Chin rest clamps are another place where RH & LH thread is used on a sleeve nut
pulling the clamp tighter..
....