Introduction
Hey there! Imagine you’re working on your ride or a project at home, and snap—you break a bolt flush with the part. Can you imagine that frustration pulse? I get it—I felt that sinking feeling too. That’s when a tool called a left hand drill bit came to my rescue. You pop it in reverse on your drill, and it can drill into the bolt and back it out simultaneously. How cool is that? In this guide, we’re unpacking what this tool does, when to use it, and tips for pulling off clean fastener extractions—even if you’re a newbie. By the end, you’ll feel confident grabbing your kit next time things snap—and know exactly what to do. Let’s dive in!
What Exactly Is a Left Hand Drill Bit?
A left hand drill bit is a twist bit just like any other—but with a twist. Instead of cutting clockwise, it drills counterclockwise (i.e. left-handed rotation). The flute spirals backwards, and it bites if run in reverse.
These bits usually come in hardened materials like high-speed steel or cobalt. You’d typically use them in reverse mode on your drill. If the bolt or fastener is broken or stuck, the rotating bit can grab and unscrew it while carving a hole inside.
How Left-Hand Bits Actually Work
Reverse Spiral Flutes
Instead of pushing debris down, left-hand bit flutes pull chips upward. That sweeping motion helps clear the hole as you drill—and reduces chances of jamming.
Pulling Torque While Cutting
When the bit bites, that reverse spiral can generate a loosening torque, pulling the broken fastener up while drilling. It’s like doing two jobs in one: cutting and unscrewing.
Ideal RPM and Pressure
Best results come at around 500–700 RPM and light pressure. Slow and steady avoids heat buildup and preserves cutter sharpness.
Main Uses & Real-World Applications
Extracting Broken Bolts & Screws
This is the most common use. When a bolt breaks off, especially in a blind hole, a left-hand drill bit drilled in reverse may actually back the bolt out. Many mechanics swear by this method:
“Left-handed drill bits are worth their weight in gold.”
“I have had more success extracting broken bolts using left-handed drill bits than any type of extractor.”
Instead of pushing the bolt deeper, reverse cutting releases it toward you.
Reducing Damage in Blind Holes
If the bolt doesn’t go all the way through, using a standard bit may wedge the fragment deeper. Reverse bits minimize that risk.
Specialty Drilling & Reverse-Thread Prep
In some CNC or screw-machine operations, where spindle direction can’t switch, left-hand bits allow continued operation. They’re also sometimes used to prepare holes for left-hand threading.
Key Benefits vs Alternatives
Drills vs Standard Right-Hand Bits
- Reduces compacting broken fasteners deeper.
- Promotes unscrewing while cutting.
- Safer for delicate surfaces.
Left-Hand vs Easy-Out Extractors
- Easy-Outs can break inside the bolt if over-torqued.
- Bit extraction avoids brittle pipe-breaking.
- Kits often include both; experts often try left-hand bits first.
Additional Perks
- Better chip removal due to reverse flutes.
- Safer speed and torque dynamics.
- Works on seized or corroded bolts with less effort.
Selecting the Right Bit for the Job
Material & Coating
Choose cobalt or HSS bits for strength—it resists heat and works through hardened metal. Some higher-end kits offer niobium alloy bits for extreme toughness like on truck-grade bolts.
Size Sets & Length
Pilot sets from 1/16″ to 1/2″ are common. Get both jobber (long) and stubby (short) versions for access versatility. Kits may also include matching extractors.
Brand Quality Matters
Cheap bits dull or snap quickly. Brands like Snap‑On, Millner‑Haufen, Drill Hog or trusted Amazon cobalt sets tend to perform reliably.
Step-by-Step Guide: Removing a Broken Bolt
Here’s how I do it—with calm precision and friendly confidence:
Prep & Clean
Wipe around the bolt, apply penetrating oil if rusted or stuck. Let it soak.
Center Punch
Lightly tap the center to guide the bit and reduce wandering.
Insert Pilot Bit
Choose a bit ~50–60% of bolt diameter. Chuck it tight. Set drill to reverse mode.
Begin Drilling Slowly
Start at ≈ 600 RPM with gentle downward pressure. Pulse on/off to avoid slip. Don’t push hard—it won’t help.
Increase Size if Needed
If no grip, step up to the next size. Just go slow, keep center-aligned.
Watch for Back-Out Movement
When the bolt starts turning, pause drilling. Grab it with pliers or wrench and unscrew by hand.
Finish Hole & Clean Threads
If residual metal remains, drill to larger bit or insert a screw extractor. Use a thread chaser or tap to clean the hole.
Post-Extraction Cleanup
Remove debris, apply lubricant to threads before reassembly.
Advanced Tips, Troubleshooting & Safety
- Heating helps: gently warm the bolt if seized—heat can expand surrounding metal and release grip.
- Use cutting fluid: keeps bit cool and flushes chips.
- Use a drill guide: for precise centering in blind holes.
- Don’t press too hard: that snaps bits. Best practice: slow speed and consistent pressure.
- Have backup bits: since they can dull or break.
- Use safety glasses: metal fragments flake off quickly.
Common Mistakes & How to Avoid Them
| Mistake | Why It Happens | How to Fix or Prevent It |
| Using standard drill (FWD) | Wrong rotation kills extraction | Always set drill to reverse |
| Skipping center punch | Bit wanders or mis-aligns | Punch a dimple to guide accurately |
| Using too high RPM | Heat builds, bit dulls | Stick to 500–700 RPM |
| Cheap bits | Snap or dull fast | Invest in trusted HSS/cobalt brand |
| Rushing without oil or heat | Bolt grips tighter or hardens | Use penetrating oil, allow soak time |
| Ignoring post threads cleanup | Won’t fit replacement bolt properly | Re-tap or chase hole after removal |
Quick Maintenance & Safety Checklist
- Use HSS or cobalt left-hand bit.
- Apply penetrating oil & center punch.
- Drill slowly at 500–700 RPM in reverse.
- Start with small pilot bit, enlarge if needed.
- Watch for bolt backing out; stop drilling when it moves.
- Use extractor only if drilling doesn’t free the bolt.
- Clean and chase threads afterward.
- Use cutting fluid + safety gear.
- Keep spare bits and tools ready.
Conclusion
There you go—your comprehensive guide to what a left hand drill bit does, why it’s so handy, and how to use one like a seasoned pro. Whether you’re saving yourself from a stripped bolt or working in tight engine bays, this tool can be a slate-clean for stuck fasteners. It was unbelievably satisfying the first time I watched a bolt back itself out of an engine head. Trust me, it felt like magic—and you can replicate that confidence next time something breaks.
With a quality bit, sensible technique, and patience, you’ve got this handled. No more cursed bolts, no stress. Just calm, controlled extraction. Go ahead, get that kit, practice this technique—and feel proud seeing stubborn bolts come out clean. You might even enjoy the process.
Please read more about the best left hand drill bits.
FAQs
Can left-hand drill bits damage surrounding material?
If misaligned, yes. Center punch and go slow. Use guides or vises for stability.
Do I need a special drill for left‑hand bits?
No. Just set your standard drill to reverse. Make sure the chuck is snug so it won’t unscrew.
What if the bolt is deeply seated?
Use stubby bits for access. Clamps or even engine removal may help. Heat is essential.
When should I use an extractor instead?
When reverse drilling fails or bolt won’t budge—but only after pilot drilling; use gentle tapping to seat extractors.
Does drilling generate too much heat for cobalt bits?
Overheated bits dull quickly. Use cutting fluid and go slow to keep them cool.