From this month's issue of American Machinist:
Charles Bates06/11/2008 I use two halves of a nut to install or remove studs. I saw the nut with threads that match those of the stud?s in half from point-to-point. Then I place the halves around the stud and grip them with vise grips to get a good hold on the stud.
From: TedinNorfolk Norfolk, U.K.
Typically I use ?easyout? extractors to remove broken studs, but if I don?t have the appropriate set readily available, the tang of a file often does the trick.
Start by drilling a hole through the center of the stud, making sure the drill diameter is no larger than half the stud diameter to avoid expanding it in the hole. Drive the tang of the file into the hole and turn the part of the tang above the stud using an adjustable wrench. If the stud does not move, try first screwing inwards, as this can break the seal. You may also need to tap the file tang in a few times more during the process. ==============================================================