Perfect screw extraction - GIF

[Frank S]

"" My absolute terror is breaking an extractor bit in the hole, .......what then?""
Then you make a trip to a really well stocked welding supply , ask for a few stud removal rods one great brand is AMTEC 264 thye are blue in color and have a tensil of up to 250,000 PSI . They have a heavy flux and are a straight arc type rod meaning the arc does not splay off to the sides at all and can with practice be used to weld out a broken stud a few inches below the surface . it works best if you can take a torch and burn off any oil and heat before welding if the stud is flush with the surface just get a washer with the same size ID as the OD of the stud weld it to the stud then Peen and peen until flat then weld a nut to the washer. while the stud and weld is hot from welding but not red spray your favorite penetrating oil around the hole until nearly cool then try to gently work the nut back and forth until loose and it come out sometimes this procedure may have to be repeated as few times before the stud is fully extracted as it sometimes will break off one thread at a time
If welding is not an option and you have already broken an extractor then a sacrificial end mill ran at very high RPMs using a pecking procedure may be your only option left to you