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The main reason as +Shauki B is mentioning in Google+ is the fact that the nut were allowing a compact design. The trick to get the nuts held in place is:

  • Get a sufficiently rigid PTFE tube. You don't want it too flexible/ductile;
  • Pre-thread the external part of the tube with thread forming tool;
  • Form a cone at the internal diameter of the tube AFTER the nut is in place;
  • Insure no debris is present that would catch the filament;
    ... You should be good to go;
    I have thousand of hours logged with this. I get probably more problem with the quick fitting (heatsink side) than with nuts.
    Good luck and give it a go...