This is a pen holder designed specifically for the Xiaomi Mijia Rollerball Pens, it features two holes that keep the pen/s at a comfortable-to-grab 60 degrees.
You will find two .stl files: one is the holder with my logo impressed on and the other is plain (so you can add your own or just keep it simpler).
I would recommend 0.2 mm, anything more than that could result in a "pixelated" slope
About 25% should get the job done
I used 2 top layers, 2 bottom and 2 side walls in order to make the print sturdy enough