[Dave at Pelican Parts]

The preferred method is generally to weld a nut onto the remaining bit of the stud. Do it as a plug weld through the hole in the nut. Then you can use a wrench to spin the broken bolt out.

You can try drilling into the bolt and using an extractor, but those are somewhat risky--they are harder than most drill bits, and they are brittle. So they can break off in the stud, giving you an even worse problem.

You can very very very carefully drill in to the center of the bolt, then drill larger, then larger, and so on, until you finally use a dental pick to pull the remaining threads out.

Or you can tow it to a shop, who will probably do one of these things.

--DD