Another auto mechanic suggestion. They make a very small hack saw. When I had a spark plug that was broken off with the threads still in the hole I would use this saw to cut through to the threads by cutting down the middle then make a cut on the opposite side.Now with a split on both sides you can use a punch and tap the pieces towards the center and lift out the pieces.Run a tap down it to clear the threads. Use antiseize so this doesnt happen again.