Alternator question

[Gray Ghost]

I upgraded my '70 during the motor swap to a one wire 1987 Silverado alternator. As with most motor swaps something always gets left untightened....aside from the lower rad hose, the jumper wire was found loose on the post today and the nut came off during the trip into or out of Dallas. Problem is that it's metric and I don't have the right thread pitch anywhere in my bolt & nut drawer.

Anyone happen to know the size and pitch I need? I know I can go in and buy several to find it, but I'd much rather know the exact size cause I have to get into the muffler shop early tomorrow morning.