Do you have a photo of the back side of that worm drive, with whatever kind of attachment is there?
It doesn't look like it's a handle (at least, not like the one on the worm drive), so I'm wondering how it couples to whatever it attaches to. That might give a clue.
FWIW, if I counted right, the handle is geared 40:1 through the worm drive. That might be a clue.