On a roll.
Finally installed the dash cam mount bracket I built from Home Depot parts in the car.
The mirror stalk on my car has very limited clearance, so the commercial mounts I’ve seen don’t work.
I bought a 1/4” thread U bolt:
Then I dremeled 5/16” off one end to allow the camera to swivel on.
The U bolt threads seem to be an exact match for the camera mount.
A second U bolt supplied a second plate. Also 2 1/4” nylon spacers, and three nuts. Put a dab of blue loc tite on all the threads and snugged it all in place.
Total cost in parts: about $4.
Seems to fit ok; will see how it holds up.