Since i have a new lathe i try to create also pens. I found this https://cults3d.com/en/3d-model/various/reusable-mold-for-pen-turning-blanks-makerneer model online.
This is a good model, but it was too big for me so i designed a smaller version.
I did not changed the original one, but created a total new one.
A good helping page is the blog page from the user where i got the original idea from:
https://www.instructables.com/id/Simple-Reusable-3D-Printed-Mold/
What i changed in my model is that i added at both ends some pins that will mark the middle and can directly used at the lathe (it is not total in the middle, because the mold wont be totally filled.
The author hasn't provided the model origin yet.