Is that what that is? Ha! I never knew! Shows what I know! I always just left that set to infinity and focused using the bellows. I assumed it was a focusing helicoil, but since only a few lenses had it, I just got into the practice of using the bellows and never really messed with it. I bought that camera used with a whole bunch of lenses and backs and no instruction manual. I did give the PDF a cursory glance once, but I admit I didn't read it over fully. I do most of my work with view cameras, so bellows compensation never really bothered me. And I've primarily just used that camera for landscapes, which are usually near infinity focus anyway. The few times I have used it for portraits were with the Polaroid back, so I never really tested it's sharpness up close. I feel kind of dumb now!By the way, I've never encountered an RB67 lens that has a focusing helicoid. Some of the lenses do have internal "floating" elements that you adjust to improve performance - primarily flat field focusing - at different distances.
That's the issue with having too many cameras. You don't get to learn all of the little ins and outs of each.