Sandie, the sanding pen

Two versions:
5mm Sandie - 119x13mm "pen" with 5mm tips that uses sanding paper strips up to 5mm width
10mm Sandie - 119x21mm "pen" with 10mm tips that uses strips up to 10mm

The length of the strips only needs to be big enough to cover the whole tip, otherwise it can be as long as you wish.
I've tested 300 to 3000 grit paper and it works fine on both. You can use higher grit for sure but I wouldn't go lower than 300 on the 5mm Sandie, it should work fine on the 10mm Sandie though.

I provided a blank tip STEP file for both versions so you can make your own tips.

Made a video to present it, it's honestly way longer than it should and the part I used to sand is not an accurate representation of an "hard part" to sand.

No hardware needed.

Happy sanding!

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Changelog:

03-06-2020
- Added lead in to the male threads, it should be much easier to start screwing now.
Thanks Chris C. for the suggestion!

19-05-2020
- Fixed the the text on the pen parts. Should be readable even with higher layer heights (tested 0.12 to 0.32mm and it works well)
Thanks Coizado for the feedback!

26-11-2019
- Re-uploaded the threaded STLs for compatibility with Slic3r. It was picking up the seperate model objects and not printing the threads. Should be working now.
Thanks Microbzz for the feedback!

21-12-2019
- Uploaded "5mm - Pen Reinforced" for those who are being unsucessful with the original version. I doubled the thread wall thickness so it should be much stronger. 
However, this makes sliding a sanding strip wider than 4mm much harder, if not impossible.
Thanks Jweaver for the feedback!