Need Help To Remove A Bolt With Stripped Head

Clamp a appropriately sized hex nut over the stripped/broken bolt/stud and weld the two together by filling up the inside of the nut. The nut will contain the weld area. The heat from the welding will also help with breaking it loose. May have to let it cool too.
 
Another +1 for left had drills. Best after heat and Kroil. If you can drill through to heat a hole, even better.

Another key I did not see mentioned. Use VERY high pressure and slow RPM. You want the drill to catch a thick chip and screw the bolt out.
 
chances of driling out without damaging the threads are slimm
helicoil is your friend..
 
One thing I've found useful when things get stuck, no matter what tool I'm using for extraction...

Put a little WD-40 or equivalent on the offender. I make a pretty good penetrating oil with a 50-50 mix of acetone and automatic transmission fluid, actually. Then let it sit and soak in for a day. The next day, hit the area with (low) heat from a propane torch. (Don't break out the oxyacetylene welder for this job...) The penetrating oil will go up in flames and the area will heat up. That's when you hit it with a blast of cool penetrating oil again and soak it back down. The combination of thermal expansion and contraction and the oil going in will start to loosen things. Plan on not being in a hurry and doing this trick every day for about a week, at which point, you'll likely have loosened things up to the point where the extraction tool you use will have a much easier job.

BTW, if for some reason you elect to drill a hole down the length of this offending screw, use a *left handed* drill bit with the drill set in reverse of its normal direction. A standard right-hand threaded drill bit with the drill going forward (clockwise as viewed from the top) is only going to drive things in deeper if for some reason the bit starts to stick and bite at all.
 
I thought I could do it but this is the result :

strip%2Bhead.jpg

The bolt is a M4 counter-sink socket-head. Before I screw it up further, I would like to seek advice from members of this forum. There are tools out there designed for extracting bolts or screws with stripped head but my impression is that they are for bolts of larger sizes so I don’t think they are the solution to my problem. I can drill out the head easily but doing so will leave the body of the bolt fully buried in the hole and I guess that will be a more difficult problem. The hole is a through hole.

May I have some suggestions pls ? Thanks in advance.

First, I would try to unscrew it using a small and sharp center punch in the exposed head of the screw. If that fails, very carefully drill the exact center with a 5/64" or 2mm bit and then with a 1/8" drill to run the 4mm .7 tap to clean the remaining threads.
 
Yes I do this to good success but at 4mm I would use a tig weld
Clamp a appropriately sized hex nut over the stripped/broken bolt/stud and weld the two together by filling up the inside of the nut. The nut will contain the weld area. The heat from the welding will also help with breaking it loose. May have to let it cool too.
No one seems to mention easy outs? often at that size I woulds insert a file tang give it a bump and unwind it if that don't work resort to welding a piece of scrap or a nut as above
 
Actually I did mention easy outs. I mentioned a few ways to get the screw out in the order I usually do. East outs were the second method of choice.
 
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