Pen designed for Pilot G-2 refills (cost less than €2) where You print just three parts and thats all - no glue, screws or tools needed. After print just insert refill into biggest body, then secure with the smallest part and You are ready to just get the Cap on, and that's all :- ) Pen is enought small to be carried in pocket and can stand itself on desk when not used.
And if You are interested to have some text on pen, let me know in msg and I will prepare You a print profile with your text.
My recomandacion is to use Bambu Lab PLA Matte, but any material can be used. Just maybe You will need little play with scale of model.
Hope You will like it!