oh you're right. Well, the size should be small - 14 knubs or less as the diameter would be perfect. The circle should be a real circle, not an egg :).
Also, the six parts must be stabil individually(and must not have to be connected to the other ones).
As you may expect, it has to turn inside of - or around - another circle(this second one does, of course, not have to be perfect). Not that easy to explain what exactly I am willing to build.