Wait a minute Mike. Are you using just a plain 510 batt? If so, I don't know if you really need an extension. I would think it would just go over part of you 510 stick if that's what you are using.
Did you catch my edit in my first post as you were responding?
Edit: Scratch that. My bad. I just realized that the cone part of the Stardust doesn't have threads. It must simply cover the ego cone threads. But that extension will work.