Rigid coupling collet

Couples two shafts rigidly by using a double headed collet with threaded nuts tightening both ends. Pretty simple, printed at 0.2mm height in PETg, 0.4mm nozzle, 25% infill. Had to add a 3mm brim on the collet to improve bed adhesion.
The picture is an earlier (but working) version that is 5mm longer. I reduced the length by 5 mm because it looks like it is plenty to have a very good grip.
Uses the threads.scad library from http://dkprojects.net/openscad-threads/

Can be quite hard to get the threads started, still looking at improving that further.
The second picture is the uploaded version. Works fine, but I broke the collet taking it apart. I need a better way to undo each single nut. Don't try and overtighten it without a matching shaft being gripped in the collet, or the collet segments will snap