I don’t know if I’m not supposed to say anything or not about it or not, but last year Vince made a few .500" to M6 adapters and I ended up with a few.
Honestly though,. I don’t use it anymore. I stopped hard mounting the bit zero and just set it on the fixture plate as needed.
I could easily resin 3d print some if you were interested though. They should be plenty strong.
I did similar to above, taking a short bit of 1/2 threaded rod and drilling/tapping it for M6 on my lathe. Though concentricity doesn’t matter, so you could probably do the same with just a drill press too
I went overboard… as per my usual. I have the original fixture plate design. I cut a recess in the phenolic slat, and notch it off the plate. I drilled/tapped a hole in the extrusion below.