The MCM arch holds the grinder handle in place which keeps it from flopping around, and keeps the grinder in the caddy. It's a really clean and easy solution for this unique problem.

I talk more about the caddy in this video if you're interested - Timestamped Link

On Friday a video will be out where I talk more about the final version (shown in the video attached to this post), but the function is quite similar, just with the correct measurements because measuring is hard...

I would be happy to share the STL, but I haven't yet as I figure not too many folks have the exact same aeropress setup as I do with the scale and grinder, and I'm lazy (but honest at least!)