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How to remove a broken bolt
Center punch the broken bolt as close to the center as possible.
Using a hammer, mark the center of the broken bolt with a center punch. This will help you drill into the center of the bolt as closely as possible, putting you at less risk of damaging the threads of the broken bolt.
Drill a pilot hole into the center of the broken bolt with the left-handed drill bit. A left-handed drill bit is threaded in the opposite direction, so the reverse setting on your drill is what will actually drive in the bit.