Fits a standard 82mm (3 1/4") diameter coffee mug. I needed a coffee cup holder that I could screw into the wall, so I modeled it up in Fusion 360. I added a left and a right facing slot for the handle. I ran out of red filament mid-print, I didn't intend for it to be two-tone.
EDIT: After uploading these, I realized that the left and right facing brackets would be nearly impossible to screw in, so I added a better version of those.