If you own a good screw-extraction kit you may have encountered left-handed bits. Left-handed bits rotate counterclockwise — the opposite direction of normal drill bits — so you drill in reverse instead of forward. Using a left-handed bit to drill out a broken screw prevents the screw from tightening further and may even extract the shank in the process.
Irwin constructs their left-handed bits with M-42, an 8% cobalt high-speed steel. They designed the heavy-duty spiral flutes to eject chips faster and the shorter 135-degree split-point cutting surface to reduce the feed pressure and torque needed to drill into hardened materials.
You’ll pay $3 to $14 dollars for a single Irwin left-handed bit, or you can buy a five-piece set for around $20.