pen for shaeffer filament

Project is not done yet. To finish it, part 2 needs to be threaded
+ There has to be added M8 metal pipe (i suggest aluminum one cause they're thicker) which will be connecting part 2 and 3 (also has to be threaded - with M8x0.75 or M8x0.5 tap and die).
+ There has to be added spring and shaeffer filament ;)