Why didn't I think of this?

[marnold***]

Hate to be a dope - but what does that spring do? Doesn't look like the trem arm threads would fit through the spring, so...??

I think (mind you, I've never had a Strat-style trem, only Floyds) that it pushes the arm against the threads in the hole so that the bar doesn't flop all over the place.