Can someone tell me what the size of the bolt/screw is that jrichker has posted below? It is for the batter pigtail and extra ground wire for a 3g alt. I think, mine just looks like a self tapping short screw that does not tighten enough when I add the ground wire for the 3g akt.
WAAAYYYY overthinking this one. Are you doing this for a concours restoration? If not get any self tapping screw that is maybe 1/2" long and fits in the hole.