I've never seen the mechanism, but that was my guess. I bet three balls ride caged in a sleeve and are backed by a collar with detents in it. When the collar is rotated, the balls engage or disengage when disaligned/aligned with the detents. I got that part of the image, but the mystery to me is how the fine threads are disengaged. Some kind of sector nut, maybe? It would have to be strong. Looks like a cool mechanism, I'm going to have to dig around for some more info. Fun!