Originally Posted by DoubleWasp
Agree. Looks like a case bolt. Any alternator bolt is going to be at least a 12mm. If it really small like an 8mm, it's almost certainly a case bolt.
Irwin Bolt Grip is the best bolt extractor I've used, but you have to hammer it on with a small sledgehammer. Don't need to hammer it like a maniac. Just helps in getting it smacked with a good short swing.
The cell phone picture may not be showing it properly nor showing the right bolt, now that I look at it. The mounting bolts are too big, IMO, to have 10mm heads but they do, for some reason.