Like Phez said. 4 little springs, each connected to the bottom of to a claw and all connected to the central claw holder. The way the co does it, with a central sprung collar doesn't work for a prop replica. That's why the co toy's claws are so hit.
I know, it's awesome :lol
I think that is actually Dan's (Anakin Starkiller) design (that is where I got that part from) and he may be able to explain how it works a bit better. There is a bunch of little springs. I can tell you it is not a good idea to take a Dremel cutting wheel to it to try to make the claws open farther. I can confirm that aspect of the design :facepalm.
Thanks for the clarification, guys. Awesome work, again!
Here, have a few extra exclamation points for good measure: !!!!!!!!!!!! :lol
-Nick
PS: Any in progress pics of the marbled shafts? I'd love to see them since so few people have shown off that particular aspect in previous builds.