That moment when a bolt head rounds off or snaps flush to the surface turns a five-minute job into a full-blown headache. The right set of hardened steel removers transforms that frustration into a clean extraction, letting you move on without drilling out the entire workpiece or resorting to a welder.
I’m Mo Maruf — the founder and writer behind The Tools Trunk. I’ve spent hundreds of hours analyzing metallurgy data, customer test results, and real-world failure modes across dozens of bolt extraction systems to separate the sets that actually grip from those that snap under torque.
Whether you are an auto mechanic fighting a seized exhaust stud or a DIYer recovering a stripped furniture bolt, this guide to the drill bits for drilling out bolts walks through the exact material grades and tip geometries that make extraction reliable instead of frustrating.
How To Choose The Best Drill Bits For Drilling Out Bolts
Drilling out a broken bolt is not a random drilling task. The bit needs to stay dead center on an uneven or concave broken surface, cut through heat-treated steel without dulling instantly, and often spin clockwise while you hope the bolt unscrews itself — which is why left-hand bits exist. Here are the specific specs that determine whether your extraction attempt works on the first try or ends with a snapped bit inside an already stuck bolt.
Material Grade: Cobalt Content Is Non-Negotiable
Standard high-speed steel (HSS) dulls quickly when it meets the hardened outer layer of a grade 5 or grade 8 bolt. M35 cobalt steel contains 5% cobalt, pushing the hardness to roughly 67 Rockwell C, which lets the bit chew through hardened fasteners without losing its cutting edge. For bolts that are already heat-treated or case-hardened, M42 cobalt (8% cobalt) offers even more heat resistance, though the bits become slightly more brittle.
Tip Geometry: 135° Split Point vs 118° Conventional
A 135° split point tip is the single most important geometry for bolt extraction. The more acute angle bites into the bolt face without skating across the surface, and the split point creates two cutting edges that meet at the center. This design eliminates the need for a center punch in most situations because the bit self-centers, preventing the walk that ruins alignment on a broken stud.
Left-Hand Bits: The Reverse Trick
Left-hand drill bits spin counterclockwise (reverse in a standard drill). When you drill a left-hand hole into a seized clockwise-threaded bolt, the cutting action itself generates torque in the loosening direction. A surprising number of bolts back out during the drilling step, saving you from ever needing the extractor. Even when the bolt does not back out, the left-hand pilot hole works perfectly with any spiral flute extractor.
Extractor Design: Spiral Flute vs Straight Flute
Spiral flute extractors dig deeper into the bolt as counterclockwise torque increases, making them ideal for high-torque bolt removal where the fastener is seized hard. Straight flute extractors rely on a friction fit inside a pre-drilled hole and work better for bolts that are already partially loose or made of softer metal. For drilling out bolts that are snapped flush, a spiral flute extractor set with matching left-hand drill bits gives the highest success rate.
Quick Comparison
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| Model | Category | Best For | Key Spec | Amazon |
|---|---|---|---|---|
| WildBossy M35 Cobalt 20-Piece | Drill Bits | Hardened steel drilling | M35 Cobalt, 67 HRC | Amazon |
| REBRA 18-Piece Extractor & Left-Hand Set | Extractor + Bits | Seized automotive bolts | Cr-Mo & HSS, 9 extractors | Amazon |
| IRWIN 11117 Spiral Flute Set | Extractor Set | Spiral flute grip | Cobalt alloy steel | Amazon |
| ENERTWIST Titanium 99-Piece | General Bits | High volume drilling | TiN coated, 1.5-10mm | Amazon |
| Roll With Us Depot 22-Piece Titanium Extractor | Extractor Set | DIY broken screw rescue | HSS 4341 & Titanium | Amazon |
In-Depth Reviews
1. WildBossy M35 Cobalt Drill Bit Set (20-Piece)
This 20-piece M35 cobalt set covers the bread-and-butter range from 1/16 inch up to 1/2 inch, which covers nearly every automotive bolt you will encounter. The 67 HRC rating means the bits maintain their edge through multiple extractions on grade 8 hardware, and the 3-flat shank prevents the bit from spinning in the chuck under the heavy torque that bolt drilling requires.
The 135° split point is the standout feature here — it grabs the center of a sheared bolt face without wandering, even when the break is uneven. Real-world users report drilling out snapped taps and studs in turbo housings, and the bits cut through thin stainless steel with slow, steady pressure. The included plastic case keeps the sizes organized, though the case itself is basic.
Where this set falls short is consistency. A few reviewers noted that some bits arrived dull or snapped prematurely under light pressure, which suggests batch QC is not always perfect. For the price, however, the bits that work perform at a level that usually costs double, making this a smart mid-range bet for anyone who needs cobalt performance without paying premium brand markup.
What works
- M35 cobalt cuts hardened bolts effectively
- 135° split point self-centers on broken surfaces
- 3-flat shank prevents chuck slip at high torque
What doesn’t
- Inconsistent QC — some bits arrive dull
- Basic plastic case offers minimal protection
2. REBRA 18-Piece Screw Extractor & Left-Hand Drill Bit Set
Rebra built this set around the concept that left-hand drill bits and extractors should work together as a system. The nine #6542 HSS left-hand bits create pilot holes that spin counterclockwise, and the nine 37 Cr-Mo alloy extractors take over for the final twist. The size range (1/8 inch to 1/2 inch bits matching extractor numbers 1 through 7) covers small machine screws through large automotive bolts.
The left-hand bits did their job in real-world use — one reviewer extracted a rounded exhaust nut in five minutes after fighting it for hours with other methods. The Cr-Mo extractors handled seizure well, though one user snapped an expander piece when using a long wrench. The 135° angle on the bits helps with starting accuracy, and the black oxide finish provides mild corrosion resistance for shop storage.
The main downside is that a few bits arrived brittle and snapped under what felt like normal drilling pressure. HSS 6542 is a step below M35 cobalt in toughness, so these bits are better suited for standard steel bolts rather than hardened or case-hardened fasteners. For the DIYer working on automotive exhausts, motorcycle drain plugs, and general household bolts, this is a capable system that earns its place through the left-hand efficiency.
What works
- Left-hand bits often extract bolts during drilling
- Matching bit and extractor sizes are intuitive
- 135° split point aids center alignment
What doesn’t
- HSS bits less durable than cobalt alternatives
- Extractor pieces can snap under high leverage
3. IRWIN 11117 Spiral Flute Screw Extractors with Cobalt Bits (10-Piece)
IRWIN’s spiral flute design is engineered with a counterclockwise helix that bites deeper into the bolt as resistance increases. This is mechanically different from straight flute extractors — instead of relying purely on friction, the spiral flute wedges into the drilled hole under torque, creating a mechanical interlock that rarely strips out. The set includes cobalt alloy steel drill bits matched to each extractor size, though the bits are not left-hand.
Real-world performance backs up the design claim. One user tried a cheap Chinese extractor for 45 minutes on a seized bolt, then the IRWIN set extracted an identical 10 Nm torqued fastener in under two minutes. Another extracted a sheared bolt after pre-drilling a center, using WD-40 and a slow constant pull with a ratchet. The extractors themselves are tough enough to handle repeated use, though the included bits are only decent — several users said the bits dull faster than the extractors.
For the price, this is a premium-tough extractor set paired with entry-level bits. The solution is to buy the IRWIN extractors and pair them with a separate M35 cobalt bit set. The spiral flute extractors themselves are durable enough to outlast several bit replacements, making this a long-term investment for anyone who regularly removes broken bolts.
What works
- Spiral flute grip increases with torque load
- Cobalt alloy extractors resist wear
- Compact pouch stores easily in a toolbox
What doesn’t
- Included bits are noticeably weaker than extractors
- No left-hand bits for self-extraction
- Small extractor head is hard to turn by hand
4. ENERTWIST Titanium Coated Drill Bit Set (99-Piece)
This 99-piece set is not specifically designed for bolt extraction, but it earns a spot here because of how frequently bolt drilling requires a wide range of metric sizes. The titanium nitride (TiN) coating reduces friction and heat buildup, which is critical when drilling into a seized fastener where lack of coolant is common. The range from 1.5 mm to 10 mm means you can step up gradually — a technique that reduces walking and prevents breaking small bits.
The 135° split point on every bit helps start on the concave surface of a sheared bolt, and the HSS base material handles mild steel bolts without issues. One user reported that after several bits broke, the seller upgraded the set to cobalt bits free of charge — indicating the manufacturer stands behind the product. The metal case is sturdy, labeled, and has extra room for other bits.
The limitation is that TiN-coated HSS is not as hard as M35 cobalt. For hardened bolts, these bits will wear faster and may require more frequent replacement, and the kit is best used as a general-purpose drilling companion while a dedicated cobalt set handles the heavy extraction work. For the price, you get volume and organization that makes locating the right size easy in a workshop setting.
What works
- 99 metric sizes cover 1.5mm to 10mm
- TiN coating reduces friction during drilling
- Sturdy labeled case with extra storage
What doesn’t
- TiN HSS lacks cobalt hardness for hardened bolts
- Some bits broke under normal drilling load
5. Roll With Us Depot Titanium Screw Extractor Set (22-Piece)
This 22-piece set is engineered for the home DIYer who does not want a drawer full of separate bits and extractors. The titanium-treated HSS 4341 steel hits 63-65 HRC, which is comfortably above standard HSS but below M35 cobalt. The extractors work with any drill, and the set covers screw and bolt sizes from 3 mm to 12 mm, making it suitable for furniture, small appliances, and light automotive work.
In practice, the set has performed well on stripped M6 torx screws secured with Loctite, and one user removed a stripped table leg screw in under a minute. The bits held up through a few uses, though one user noted slight wear after extracting two M6 screws — not surprising given the 4341 steel, but worth noting if you are extracting bolts regularly. The compact case fits in a toolbox drawer, and the set is gift-packaged with wrap available.
The key trade-off is that the titanium coating on 4341 steel does not match the toughness of a dedicated M35 cobalt drill bit or a spiral flute extractor from a premium brand. For occasional use on unhardened fasteners, this is a convenient all-in-one kit. For heavy-duty automotive or industrial extraction, the bits will wear faster and the straight flute extractors may slip on extremely seized bolts.
What works
- All-in-one kit for quick bolt removal
- 63-65 HRC handles standard fasteners well
- Compact storage and gift-ready packaging
What doesn’t
- 4341 steel less durable than M35 cobalt
- Bits show wear after a few extractions
- Not ideal for heavily seized or large bolts
Hardware & Specs Guide
M35 Cobalt vs HSS vs TiN Coated
M35 cobalt steel contains 5% cobalt, giving it a hardness of roughly 67 HRC that maintains its edge through hardened bolts and high heat. Standard HSS (around 62-64 HRC) dulls quickly on case-hardened fasteners. TiN-coated HSS reduces friction but does not add core hardness — the bit steel underneath still wears against hard bolts. For drilling out bolts that are already hardened, M35 or M42 cobalt is the only reliable choice.
135° Split Point vs 118° Point
A 135° split point creates two cutting edges that meet precisely in the center, letting the bit start drilling without a center punch and without walking across the bolt face. The 118° conventional point tends to skate on uneven or rounded surfaces, which is why split-point geometry is mandatory for bolt extraction. Split-point bits also produce smaller chips, reducing clogging in deep holes.
Straight Shank vs 3-Flat Shank
Most drill bits use a smooth cylindrical shank that can spin in the chuck under the high torque loads typical of bolt extraction. A 3-flat shank has three ground flats that the chuck jaws grip securely, eliminating the spin that ruins alignment and wastes time. For any kit intended for drilling out bolts, 3-flat shanks reduce frustration significantly.
Spiral Flute vs Straight Flute Extractors
Spiral flute extractors have a counterclockwise helix that digs into the bolt as torque increases — the harder you turn, the deeper they grip. Straight flute extractors use a tapered, fluted shaft that wedges into the pilot hole. Spiral designs are superior for seized or rusted bolts because they do not rely solely on friction. Straight designs work well for bolts that are already slightly loose or made of softer metals.
FAQ
Should I use left-hand drill bits or right-hand bits for bolt extraction?
What is the difference between M35 and M42 cobalt for drilling bolts?
Final Thoughts: The Verdict
For most users, the drill bits for drilling out bolts winner is the WildBossy M35 Cobalt 20-Piece Set because the M35 cobalt, 135° split point, and 3-flat shank deliver the perfect balance of hardened-edge durability and self-centering accuracy for the widest range of fastener types. If you want the advantage of left-hand bits that often remove bolts during the drilling step, grab the REBRA 18-Piece Extractor Set. And for the mechanic who needs spiral flute grip that tightens under torque, nothing beats the IRWIN 11117 Spiral Flute Set.