Ahhh, that does make sense! ... I think I have it. So basically that centre piece is actually off centre in terms of the head as your drawings show. The holes that will be in the brass rings with also be off centre so as you spin the rings, they will not allow the centre piece down until they are rotated to align the bore with the centre piece.... think that makes sense. As your spinning them and pushing it down, you`ll feel it fall through when you get each into the right position..... I like it!
....after all that, they still have to rotate the centre piece to align the hole and then align the top and bottom pieces of the cylinder and give it a bit of a shake to release the balls...ouch!
My mother in law did actually complete my Mk2 puzzle but it took her a couple of nights of doing it during TV watching for her to get it open.
I can`t wait for you to start this!! So I presume the plan is to continue with the CNC one as well?