Ooo, some of you are very good at this, and fast too. On the other hand, I did catch out a fair few by duplicitously hinting at adjustability. We'll call it a score draw.
Yes, the mystery pic didn't show the parts fully "home" so I could lead you astray with thoughts of patented augers and such, but here it is, fully locked and not quite such a close up.
#46758594: Make key for take-down square.
Anyway, now you car boot and flea market types know to start looking out for ratty canvas pouches now as well as more obvious rust - you never know what you might find inside. And thanks for for playing along and taking a guess!