I needed a secondary Arca Swiss mount to mount the EF to EOS-M adapter on the tripod, so that all the weight would not hang off the camera unsupported. I found many models but they all seemed way too much bulky for my taste, so I decided to design it myself.
I made it small since the adapter tripod mount has this width anyway, so it would have been useless to make it bigger, and this way I can keep the original one on the camera, as they don't interfere with each other, and use one or the other depending on whether I'm using the kit lens or an adapted one.

I printed at 0.2mm with 50% infill to make it pretty robust. It's probably overkill if you're not using the biggest lenses out there, but better safe than sorry, it's a small piece anyway, so you're not wasting that much filament.

PLEASE NOTE: Best to print upside down (rotate 180° on X axis) so it doesn't need supports. The dovetail is at 45° so it should be fine on any printer