They can most definitely be a crapshoot. Over the years I have had much more success with the stubby style as opposed to the long, narrow and somewhat flexible ones.

 

I can't say that I've ever had one fail me... somehow I've always managed the moxie to get that broken POS out!!

Patience and tenacity is the key. Also, quality ez outs. Nothing from HF or Homey Depot. Napa or a local tool supply house will
get you a better kit.

 

 

The moment you put you were trying to remove a broken exhaust stud I knew what was coming.

There is a proper tool for drilling through a stud and then re-tap the thread.

 

Just about all tools have a job they were designed for. Get outside of that envelope and it gets dicey. Quality is where is at, as said.

I drill the hole with a left handed, that might bring it out, doubtful but has happened. Easy out, right size for the bolt, in the right size hole. The REAL secret is knowing when theory and reality collide. A easy out may NOT take the bolt out, period. Then I step the drill sizes up so I can gently get the hole as close to center as I can, ending at the trap drill size. Then you MIGHT be able to use the correct tap to peal the bolt threads out of the threads in the hole.

If all that fails then you are very close to the correct position of the hole so drill it for the tap drill size for a Helicoil and set one.

Broken bolts suck, some suck a LOT.

 

Read what Lakerat said and believe it. THAT is THE penetrating fluid for any screw joint. Its been more than a decade since I read it, but there was an ASE study/experiment that tested various commercial penetrating oils in the lab. All the popular brands everyone swears by. They included this old homebrew concoction for laughs... and it outdid all the commercial stuff by a wide margin. Best part is you can make a gallon for about $10!

 

next time try drilling the correct size hole and use a allen wrench driven in slightly

 

Never had an issue myself, it's all about patience. Saved me a few times. Like anything, usually the user unless you have junk tools.

 

Dang, man. How big is your head?
Judging by the helmet in your sig pic...............

 

Good one.