Bought these as I snapped 2 brake caliper mounting bolts on my car (m10 bolts). Ground the top of the stud flat, drilled a suitable sized hole, hammered in the biggest extractor and heated the whole stud with a blow torch and loosened the extractor with a big adjustable spanner. Broken bolt released finally. I should note if you're going wrong with these, try and use the biggest extractor possible, the small ones look like they would snap.
Out of the 6 screws I attempted to use these on, only one was retrieved with great difficulty. Regret giving my old set away.
