I produced these files for the excellent CrushGrind 25 mechanism. The mechanism is readily available from Amazon and many others.
These files are provided as a tested template that you can use in your own pepper mill design. Subtract these files from your design to fit the CrushGrind mechanism. The tool stl is used to assist in pressing the bottom mechanism into place if you desire. This is designed with pretty tight tolerances (you don't want the mechanism slipping) so you might want to make a test print first and adjust as necessary.
There are two top designs. One is low profile but may need supports. The other can be printed without supports. The main mechanism needs support only for the bottom rim. Set supports to touching build plate and 45 degrees and you should be good.
I am also uploading a pepper mill made with these files to demonstrate that they work. www.thingiverse.com/thing:3090539
The design is available on Onshape https://cad.onshape.com/documents/4487c204ce73b189b984f887/w/13b5355c94616d2c05a6f16d/e/5f65ae8d6b5f238627822e62