If you look closely the picture it might just be a base/stand the ProVari is sitting on. It doesn't seem very practical to have a screw on base that large.
ETA: Oops! I thought you meant the wide part, not the bottom cap.
Is it sitting on something not attached?
Yeah, was talking about the really wide part..
Possible to solder that onto the bottom, maybe, and still change out the battery?
And for home use, I find it very practical..