Not only do these rings do the job as intended, they are beautiful to look at. I use them as "memory locations" for my guiding camera and my planetary camera. I never hunt around for focus, juts slide the camera into the focuser, the ring places it at the correct point.

They work just fine. I’ll be replacing the tiny set screws with some thumb screws so I don’t have to fiddle with a tiny hex wrench in the dark.