At first glance the Delta reminded me of the first puzzle I ever wrote about, the Cast News. It has that same sort of enclosed container look about it, except where the News is an extremely rattly puzzle, the Delta feels much more solid in the hand.
Now from this position it is easy to close the puzzle fully, then re open to this point, then close it again....then semi-open it again etc. This is the point where it seems most puzzlers get a little bit stuck.
I had a feeling that coordinate motion would be the solution to this puzzle, but when I spun it nothing happened, and when I pulled them all against each other at the same time...nothing happened. There was clearly something that I was missing.
It's not a particularly difficult puzzle, with most people I have spoken to solving it within 5-6 minutes, but the elegant design makes it well worth owning. Plus it's a great one to hand over to non-puzzlers, since it has an obvious solution and they are likely to be very pleased with themselves when they solve it...plus it's practically invincible in case someone gets really fed up and throws it out of a window.
The Hanayama Cast Delta is currently available from Puzzle Master and all other good puzzle distributors.