Got up off the couch and measured mine.
Small stud is definitely 4mm diameter with a 7mm head. (These are Denso starters so think Japanese.)
Large stud measured 7.05 mm but honestly I think it's 5/16"-18. I tried that size nut on the exposed threads and it seems to thread on easily. Both a 13mm and 1/2" socket fit the head.
The negative goes to ground, no negatives get screwed to the starter! Do you really know what your doing????? I venture to say otherwise, Don't burn it down!!!