There are some ready-made surface pen case in makerworld, bue none of them meets my requirements - some of them are too big, some of them are in irregular shape, even some of them cannot protect the pen tip! so I made my own one.

Please notice that This model has very precise dimension, it should exactly fit a surface pen, meaning that the pen can insert into the case smoothly with little but exist fraction, and the cap and base should close without gap (just like there is no pen inside), and you will unable to hear the pen hitting the model's inner walls when you shake it.

I use PETG, any changes to materials and printing parameters may result in changes in the shape of the finished product. The 3mf file fills in the slowest print speed, you can use it as-is, or print at 166%speed or a little faster, so that the model will have a moderate amount of brushing inside to provide cushioning.