knurled pen

I designed this thing for people with sensitivity issues after a stroke. You just have to recycle a BIC pen refill.
Compared to a normal pen, it allows a better grip thanks to its increased diameter and the knurled part gives a more sensitive sensation when writing.

UPDATED 11/15/2018 :
- added version with small hole.
- added model with smoother pattern (d13), thanks [Hexamus](https://www.thingiverse.com/hexamus)

UPDATED 09/08/2018 :
- added fusion360 and STEP files for remix as aske