Stud Extractor (Screw Extractor)

Some grip the outside of a stud; others are drilled into a broken bolt. Left-hand drill bits sometimes unscrew the bolt while drilling. Penetrating oil and heat help first. Welding a nut onto a broken stud is another common way to remove it, as the heat also helps.

Its tapered, reverse-threaded or gripping design bites into the fastener and turns it out.

Extractors are hard and brittle; a broken one is very hard to remove. Use steady force, not impact.