They look almost identical to standard bits, but they cut in the opposite direction. Left hand drill bits spin counter-clockwise, and that single difference makes them invaluable for extraction work.
What Makes a Left-Hand Bit Different
A conventional right-hand bit cuts when the drill turns clockwise. A left-hand bit has its flutes ground the opposite way, so it removes material only when the drill runs in reverse. Set most cordless and corded drills to reverse and the bit cuts normally, just in the mirror-image direction. Everything else about the bit, from the shank to the point, works the same way you already expect.
The Killer Application: Broken Fasteners
The real magic happens when you drill into a broken bolt or stud. As the left-hand bit bites in reverse, its counter-clockwise motion tends to grab the seized fastener and thread it out on its own, often before you even need an extractor. That is exactly why they are a staple in every mechanic and repair kit, and why they save so much time on rusted or snapped hardware.
- Self-extracting: The reverse cut frequently backs out the broken piece unaided.
- Centred start: Punch and centre the hole so the bit stays true in the fastener.
- Pair with an extractor: If it does not free itself, the clean hole is ready for a screw extractor.
How to Use Them
Set your drill to reverse, mark and centre punch the broken fastener, and apply steady pressure at low speed. Add penetrating oil to the seized threads first and give it several minutes to work its way in. Let the bit cut gently, because the goal is to catch and unwind the stud, not to power straight through it. If it starts to spin the stud, keep going and let it walk the fastener out.
Beyond Extraction
While extraction is their headline use, left-hand bits also help in machining situations where clockwise rotation would loosen a workpiece or threaded fitting. For most home and shop users, though, they earn their keep rescuing snapped bolts and stripped studs that would otherwise mean drilling out and re-tapping the hole entirely.
Choosing Quality Bits
Because extraction puts real stress on a bit, material and grind quality matter a great deal. Cobalt and premium HSS left-hand bits resist the heat and torque of digging into hardened, seized fasteners without dulling or snapping. American-made bits give you the toughness this demanding job really needs.
