As I posted earlier in this thread, heat is the only way. Especially when a steel stud/bolt is in aluminum. The way to look at it , all of this drilling/extractors/etc is after you have failed.
I have an oxyacetylene torch and typically use a large welding tip. Heat the bolt/stud itself cherry red. Let it cool until the color is gone and try to remove it. Do not try hard or aggressively. Reheat and try as many times as necessary.
Most do not have the ability or means necessary to remove things broken flush. If it is an expensive piece, take it to a competent machine shop. Piece of cake for them. Most have no way to drill the center of a flush break.
This episode has traveled a predictable path.
edit- I see this is a new thread. Same topic and I believe the same poster.