There is quite a history contained in this little puzzle. The Cast Ring is based on a 15th century European puzzle, and this style was actually used for official engagement rings. Christian reformist, Martin Luther, was known to wear one. It is also rumored to prove as evidence of its wearer’s adultery...when it comes apart into pieces.
This version is approximately 5cm in diameter, so it's not a piece of jewellery, but is quite a tricky coffee table puzzle. NOB.
Separate? OK! but mostly; put back to start! (That's the real challenge)