Summary

This is a filament spool assembly, for a "Hongdak" 3D Pen. (Purchased from Amazon). This spool easily holds about 4 feet (1.3m) of filament.

When joined together, the gap around the outer edge will be near 1.75mm wide. Smooth over any sharp edges on that gap so the filament feeds easily, without snagging.

Test fit the two halves. File down any imperfections where the two halves mate. Glue, or use your 3d pen to weld them together. Welding is easy, fast and strong.

Cut a length of filament. Feed one end into the gap between the halves, and wrap it around and around.

The pen has air vents. My pen seems like it was built for a left-hander, so I hold it a certain way. I designed the arm so the vent-cut-out is in back. The pen's vent holes are facing rearward. This way, I can see the LCD screen while working, and use my thumb to operate the filament feed buttons.
Modify the arm file if required. Bottom line is the air venting keeps the electronics cool, so try not to block vent holes.

0.3mm layers with a raft. Afinia printer.
Two halves of a spool required 60 minutes, 22g ABS.
An arm needed 30 minutes, used 11 grams.
Metric files provided. If you import microscopic files, try the Metric versions.