pull the end plate off and look at where the stud passes through the case. be careful, as the cover is spring loaded, and covers the contactor set [that most likely is not the correct name, but i have always called them that] that actuates the starter when you supply 12v to the small post. think of it as a relay setup. you should see a bolt head with an eyelet attached to a wire going into the guts of the starter. if so, tightening that bolt [with the outside nut] will tighten that stud, and you should be back in business. just be careful you don't crack the isolator bushing.
however, if you find the wire going into the guts has been soldered to that stud, and has broken off from spinning the stud, it's time to put it back together and return to the parts store.
it sounds lots harder than it really is. hope this helps.