I picked these up today so I could try to remove my busted bolt in my head. I was told that these were the strongest "easy outs" they had. Chrome Vanadium Steel...I also picked up two drill bits and was told they would drill grade 8 bolts.

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they work, just dont break them in the hole

 

Yep... I have a set of those. Much better than the "helix" style. They work pretty good. just make sure to soak the broken bolt/stud in PB-Blaster beforehand.