The Natural Philosopher wrote:
Abd of course the stud extractor - a reverse threaded self tap
screw with a socket top...it screws in to any hole anti-clockwise
and jams there. Used for pulling broken studs out of almost
anything.

Useful for extracting non-siezed broken threaded components -
otherwise useful for jamming undrillable fragments of hardened
steel in holes drilled in siezed broken threaded components.


J.B.