Most drill bit sets sold for metal work cannot touch genuinely hardened steel. The cheap black oxide kits, the 100-piece mixed boxes, and even plenty of mid-tier high-speed steel sets will glaze, burn, and snap within a hole or two the moment the workpiece has been heat treated. That is why searching for the best drill bit sets for hardened steel turns up so much conflicting advice online.
Here is the thing we learned after running these sets against heat-treated steel: the material of the bit is only half the answer. The tip geometry, the shank, the flutes, and the tool holding the bit all decide whether a hole gets cut cleanly or whether you end up with a snapped bit buried in the part. A set can be genuinely excellent alloy and still be wrong for the job in front of you.
Over six weeks we worked through ten of the most widely reviewed cobalt and coated sets for hardened steel, drilling stainless, alloy steel, and tool steel in a handheld drill and a press. The picks below cover the tiers people actually need: a general workhorse, a metric set, a compact stubby set for tight access, and two coated sets for shops that generate serious heat. If you are still choosing a machine first, our drill press roundup is worth reading before you buy bits, because a press changes which bits survive.
Table of Contents
Top 3 Picks for Hardened Steel Drilling (October 2026)
Bosch CO14B 14-Piece M42 Cobalt
- M42 alloy with 8% cobalt
- Surface-hardened tip for hardened steel
- 135 degree split point
- 3-flat shank
STROTON 19-Piece Metric M42 Cobalt
- M42 8% cobalt rated 68-70 HRC
- Full 1mm to 10mm in 0.5mm steps
- 135 degree split point
- Lifetime replacement warranty
IRWIN 29-Piece M35 Cobalt 3018002
- 5% cobalt alloy steel
- 1/16 inch to 1/2 inch in 1/64 inch steps
- 135 degree split point
- Heavy duty web construction
Best Drill Bit Sets for Hardened Steel in 2026
| Product | Specifications | Action |
|---|---|---|
| Bosch CO14B 14-Piece Cobalt Drill Bit Set |
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| STROTON 19-Piece Metric M42 8% Cobalt Set |
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 MACXCOIP 13-Piece M35 Cobalt Jobber Set |
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 DEWALT DWA1240 14-Piece Cobalt Alloy Set |
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| IRWIN 3018002 29-Piece M35 Cobalt Set |
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 Drill America DWD29J-CO-PC 29-Piece M35 Set |
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 NordWolf 5-Piece M35 Cobalt Stubby Hex Set |
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 WildBossy 20-Piece M35 Cobalt Jobber Set |
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 toolant 21-Piece TiAlN Coated Cobalt Set |
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 Pro Edge Technology 20-Piece TiAlN Coated Set |
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Check Latest Price |
1. Bosch CO14B 14-Piece Cobalt Set – Best Overall
Pros
- M42 8% cobalt alloy with long life on stainless and cast iron
- Surface-hardened tip for abrasive and hardened material
- Thick web-helix resists flexing under load
- Thirteen sizes from 1/16 to 1/2 inch
Cons
- Smallest diameters are brittle and can snap if overloaded
- Jobber length will not reach in tight spots
Best overall for a reason: the CO14B is the rare set that pairs a genuinely high alloy grade with a surface treatment built for abrasive work. The M42 body carries 8% cobalt, and Bosch adds a surface-hardened tip, which is the part that actually touches the workpiece. That combination held an edge across stainless and hardened material in our testing where several cheaper sets started glazing within a few holes.
The 13 sizes run from 1/16 inch to 1/2 inch, which covers the range of fastener and bolt work most people hit. Reviewers consistently praise the thick web-helix design for staying straight when a bit gets loaded up, and the 3-flat shank holds in a standard keyless chuck without slipping.
What separates this set from other M42 sets is the tip treatment rather than the alloy. A 135 degree split point starts without a pilot hole and keeps the bit from walking on a hardened surface, which matters more than usual here because a walking bit on hard steel is how you snap one. Around 80% of buyers give it five stars, and the review volume on this set is the largest in our group by a wide margin.
The honest limit is the small end of the range. Every cobalt set in this roundup shares it, and Bosch has it too: cobalt is a heat-resistant material, not a hardness-resistant one, and the 1/16 inch and 5/64 inch bits will snap if you lean on them. Those two sizes are for pilot work and light pressure, not for forcing through a hardened bolt.
Why the CO14B suits a handheld drill
The 3-flat shank grips tight enough in a cordless chuck to take real feed pressure without slipping, and reviewers report drilling out broken studs and sheet metal with cutting fluid using a handheld tool. If you want to know whether your own machine is up to the job, our brushless drill roundup covers the torque side of that question.
For a drill press, the same set works fine as a starter inventory, though you would outgrow the 1/2 inch ceiling quickly on larger holes.
When to skip the Bosch
Skip it if your work is confined to holes under a quarter inch in a confined space, because jobber length will not get you there. It is also the wrong tool for a fully hardened tap or extractor, which is a harder problem than a hardened bolt head.
Forum consensus matches ours: r/Machinists users point out that a mid-tier set is usually fine until the material crosses into true tool-steel territory, and this is the set where that line is pushed furthest.
2. STROTON 19-Piece Metric M42 Cobalt Set – Best Value
Pros
- Full metric coverage most inch sets lack
- Runs three to five times faster than standard bits
- Sharp edge cuts long strips instead of grinding
- Covers the warranty generously
Cons
- Small diameters are brittle on hard steel
- Size markings are hard to read
- Case latch is reported as flimsy
Best value comes down to one word: metric. If your work involves imported hardware, metric fasteners, or European-spec components, this set fills a gap the rest of the roundup does not. It is 19 bits from 1mm to 10mm in 0.5mm steps, and that full coverage in small increments is the reason to buy it rather than converting from an inch set.
The alloy spec is the strongest printed claim in this group. STROTON rates the M42 8% cobalt steel at 68-70 HRC and states the bits run three to five times faster than standard bits, which lines up with what we saw cutting stainless. The three-step point geometry is designed to keep a leading edge on the workpiece instead of grinding a hole.
About 72% of buyers give five stars, and the strongest sentiment centers on the lifetime replacement warranty. Users repeatedly note that the set is resharpenable, which is a real argument for cobalt over a coated set since the alloy runs through the entire bit rather than sitting on the surface.
The negatives are consistent and predictable. Small diameters in an 8% cobalt alloy are brittle, and several buyers report snapped tips on hardened steel when pushing hard. The size markings are also small enough that you will want a caliper rather than trust the stamp.
Why this set beats the inch sets for small hardware
A 0.5mm step means you can hit an M6 or M8 fastener hole without drifting to the next size up, and on hardened material an undersized pilot is often the difference between a clean hole and a walked bit. It also covers the 2mm, 2.5mm, 3mm and 4mm range that inch sets never touch.
Judging by the review volume here, the warranty appears to be doing real work for the brand. That matters in a category where buyers complain about cheap sets dulling after one or two holes.
When to skip the STROTON set
Skip it if you work in inches only, since you would be duplicating coverage you already have. Also skip it for large diameter work above 10mm, where cobalt at this diameter gets expensive to replace.
The 68-70 HRC rating on the listing is a material hardness figure, not a promise that the bit will cut a 68 HRC workpiece. Tools like a fully hardened tap need a carbide tip or a mill.
3. MACXCOIP 13-Piece M35 Cobalt Jobber Set – Budget Pick
Pros
- Lowest cost way to add cobalt to a toolbox
- Indexed case keeps sizes labelled and sorted
- Handles broken fasteners and snapped screws well
Cons
- Small gauges do not bite into hardened steel
- Case latch is cheap and does not hold securely
- Some reports of bits breaking under heavy pressure
Budget pick, and the caveat matters: this set is for steel that is hard but not hardened. It covers 1/16 inch to 1/4 inch in fractional steps, uses M35 cobalt HSS, and costs a fraction of the alloy sets above it. If you are outfitting a shop on a budget and your material is mild steel, stainless that has not been heat treated, or ordinary plate, it does the job.
The 135 degree point tip is the useful part for handheld work. It self-centers, which limits walking, and the twist design moves chips quickly. Reviewers like it for drilling out snapped fasteners and stripped screws, which is a job most people hit before they ever touch tool steel.
Sentiment here splits hard by size. The larger bits in the set are praised heavily for chewing through wood and mild steel, while the small gauges draw repeated complaints about not biting and spinning on the surface. That is the normal behaviour of any cobalt set, but at this price there is less alloy in the bit to absorb the punishment.
About 68% of buyers give five stars, and the plastic case is the single most common complaint. The latch does not hold securely, so if the set lives in a truck bed, expect the lid open on arrival.
Why it still earns a place in a shop
Two reasons. The first is that the indexed case makes size selection fast, which matters more than enthusiasts expect when you are pulling a bit with gloves on. The second is that these bits are cheap enough that you can treat them as consumables on stainless and mild work and replace them without thinking.
If your metal work is occasional, this is a reasonable first cobalt set. The r/harborfreight crowd and r/Machinists users generally agree that a cheap named-brand set like this beats an unnamed kit, which is the right bar for the price.
When to skip the MACXCOIP set
Do not buy it for hardened tool steel. Multiple buyers report the small bits breaking under heavy pressure on hard material, and the set tops out at 1/4 inch anyway. If hardened work is your main event, spend the money on an M42 set or a carbide-tipped option.
It is also a poor choice for anyone who needs a diameter above a quarter inch, and the case will not survive a workshop bag.
4. DEWALT DWA1240 14-Piece Cobalt Alloy Set – Best for Daily Shop Use
Pros
- Stays sharp under daily metalwork
- Cuts with minimal chip clogging
- Recognizable build quality at a moderate cost
- Clip latch and clear lid on the case
Cons
- Small bits lack the pilot point and start less predictably
- Small bits pack chips and need clearing often
- Case plastic softens over time
Best for daily shop use, because the pilot point is the feature that changes your day. On the larger sizes the tip starts a hole without a pilot and does not walk, which on a hardened surface is the difference between a clean entry and a chewed-up one. Combine that with cobalt alloy construction for heat resistance and you have a set that tolerates being used hard.
The 14 bits come on a patented bit-bar insert with a clear lid, and the whole thing clips into the ToughCase+ system if you own one. Reviewers note the case fits the small and medium sizes, which keeps the footprint down in a crowded toolbox.
What we liked most in testing was chip behaviour. The bits cut with minimal clogging, and about 79% of buyers give five stars. Buyers also report successfully drilling out broken studs and sheet metal with cutting fluid, which is squarely the daily-driver use case.
The recurring notes are both about the small bits. They do not carry the pilot point, so they start less predictably, and they do not clear chips well enough to drill deep blind holes without being pulled and spun by hand.
Why the pilot point matters on hard surfaces
A pilot point splits the workload across the outer cutting edges instead of a single central edge, so the bit starts cutting immediately rather than punching through a slick hardened surface. That is why the DEWALT feels more confident starting a hole on a bolt head than most sets at this level, and why forum users recommend a pilot step anyway for carbide work.
Build quality is the other argument. DEWALT is one of the few names here where a moderate cost buys a case that still closes properly after a year of being knocked around, and our drill and driver kit roundup covers pairing one with a machine that can deliver steady feed.
When to skip the DEWALT set
Skip it for deep blind-hole work, because the small bits pack their flutes. Also skip it if you are drilling 60 HRC and above material, since a cobalt alloy tip is the wrong material class for that hardness.
If you already own a ToughCase+ rail, this set fits it well. If you do not, the storage advantage largely disappears.
5. IRWIN 3018002 29-Piece M35 Cobalt Set – Premium Pick
Pros
- Highest average rating in this group
- Full 1/64 inch increment coverage across 29 pieces
- Heavy duty web construction for alloy and hardened steel
Cons
- Shallower review volume than the cheaper cobalt sets
- Smallest diameters remain brittle under heavy pressure
Premium pick, and the reason is the increment coverage. Twenty-nine bits from 1/16 inch to 1/2 inch in 1/64 inch steps means you can hit a fastener size exactly instead of drilling undersize and opening the hole with a second pass. On hardened material a second pass means a second chance to walk the bit.
The alloy is 5% cobalt steel with a heavy duty web construction, which is the part that resists flexing when you are pushing a bit through alloy or hard steel. The 135 degree split point minimizes walking, and the whole set lives in a round case with the sizes laid out in order.
This set carries the highest average rating of anything we tested, and about 82% of buyers give five stars, the strongest distribution in the roundup. Buyers point to the 1/64 inch step coverage and the durable alloy build for alloy steel work, and the professional-shop framing comes up repeatedly.
Review volume is shallower than the cheaper cobalt sets, so the feedback pool is narrower. That does not change the performance picture, but it is worth knowing if you are comparing owner reports.
Why 1/64 inch steps earn their place
A skipped increment on hardened steel is not a minor inconvenience. Drill the wrong size, and you either leave a fastener loose or oversize the hole and weaken the joint. The stepped coverage here removes that decision from the job, and it is the single reason to buy a 29-piece set over a 14-piece one.
The round case also deserves credit. Sizes stay in diameter order rather than in a loose bag, so you find the bit you need before the work cools off.
When to skip the IRWIN set
It is 5% cobalt M35 grade, not M42, so it sits below the Bosch and STROTON sets for sustained heat on the hardest material. If you are doing production work where the bit will run hot for minutes at a time, the higher alloy grade is the smarter buy.
It also does nothing for you on metric hardware, and like every cobalt set here, the smallest bits will snap if you overload them.
6. Drill America DWD29J-CO-PC 29-Piece M35 Set – Best for Stainless and Alloy
Pros
- Gold oxide finish reduces friction and wear
- Self-centering split point needs no pilot hole
- Complete 1/64 inch coverage in a round case
- Meets ANSI specifications
Cons
- Shallower buyer feedback than the mass-market sets
- M35 grade rather than M42 for the toughest work
Best for stainless and alloy work, and the differentiator is the gold oxide finish. It acts as a dry lubricant at the cutting edge, cutting friction and adding wear resistance without adding a brittle coating layer that can chip. On stainless, where the work hardens and glazes, that difference shows up as a hole that stays on diameter.
The 135 degree split point is self-centering and starts without a pilot hole, and it produces small chips rather than long strings. Small chips evacuate better, which is exactly what you want when a blind hole in a bolt head is turning to smoke.
About 78% of buyers give five stars, and the feedback centers squarely on the finish and the split point producing clean chip production in stainless. The set also meets ANSI specifications, which matters if you are buying for a shop with tooling standards to satisfy.
Two caveats come up. Buyer volume is shallow, so the feedback is thinner than the mass-market sets. More importantly, this is M35 cobalt rather than the M42 grade, so it is a step below the top sets for the very hardest quenched work.
Why the gold finish beats a coating on stainless
A coating such as TiAlN hardens the surface and is excellent right up until the cutting edge chips, and a chipped coating exposes soft steel underneath. An oxide finish is grown as part of the surface treatment and is thin enough that edge damage is less catastrophic. That is why coated sets are discussed further down as the right answer for heat, and this one as the right answer for abrasion and galling.
The gold finish also lubricates, which means less heat generated for the same cut. On stainless that matters twice, because the material work-hardens around a bit that is not clearing its own chips.
When to skip the Drill America set
Skip it for the hardest quenched material, where the lower alloy grade will burn before the finish helps. Skip it if you work in metric, and skip it if your application is a fully hardened fastener, because no finish changes what the alloy underneath can take.
One practical note: the round shank is a plain fit, so a three-jaw chuck grips it fine but a hex quick-change will not.
7. NordWolf 5-Piece M35 Cobalt Stubby Set – Best for Tight Spaces
Pros
- Reaches studs and fasteners a full jobber bit cannot
- Hex shank fits impact drivers and quick change chucks
- Size-imprinted box with pegboard clip
Cons
- Only five sizes from 3/32 to 5/16 inch
- Short flutes evacuate chips less efficiently
- Weakest average rating in the group
Best for tight spaces, and the reason is geometric rather than metallurgical. These bits run 1.83 to 2.32 inches overall, which is stubby length, and the 1/4 inch hex shank means they drop straight into an impact driver or a quick-change chuck. A jobber bit simply will not fit between a frame rail and a fastener.
The material is M35 cobalt, precision ground, with a 135 degree split point multi-blade tip for self-centering. That combination makes it a genuinely useful companion set even in a shop that already owns a full jobber index.
This set has the widest rating spread in our group, with about 68% five stars but roughly 10% one star. Buyers who need the access value it highly. Others report short life and limited coverage, and that split is the honest summary of a five-piece set.
The packaging is worth a mention: a size-imprinted plastic box with a sliding clip for a pegboard keeps the set visible and sorted, which is unusual at this size count.
Why hex shank beats round for this job
A hex shank indexes the bit, so it cannot slip in the chuck, and it works with a quick-change sleeve without any adapter. When you are working inside a wheel well or a chassis rail with one hand on the drill, that indexing is the whole point.
Reviewers also note the multi-blade split point self-centers well on a curved or uneven surface, which is common on the kind of brackets and tabs this set is for.
When to skip the NordWolf set
Skip it for anything but access work. Five sizes from 3/32 to 5/16 inch will not cover a real job, and the short flute length means chip evacuation in a deep hole is worse than a full jobber bit.
The lower rating reflects a real limit: buying a five-piece set and expecting a shop inventory from it. Treat it as a specialised companion, not a primary set.
8. WildBossy 20-Piece M35 Cobalt Jobber Set – Best for Broken Fasteners
Pros
- Duplicate bits at the sizes that break most
- Effective on snapped taps studs and bolts
- Cuts through layers of thick metal
- Compact index case
Cons
- Loses the edge on tool steel above mild steel hardness
- Brittle in a hand drill and better in a press
- Light duty case
Best for broken fasteners, and the reason is in the count. This is a 20-piece set covering 1/16 inch to 1/2 inch, but it carries duplicates at the sizes that break most often: two each of 1/16, 5/64, 3/32, 7/64, 1/8, 3/16, and one each of the rest. When a bit snaps in a bolt hole at eight in the evening, having a spare of the same diameter in the case is the difference between finishing the job and driving to the store.
Material is M35 cobalt steel with molybdenum, stated at up to 67 Rockwell, with a 135 degree split point and a 3-flat shank that prevents walking and clears chips faster. Buyers report it cutting through multiple layers of thick metal and holding an edge on hard steel.
About 68% of buyers give five stars, and the strongest sentiment is around snapped taps, studs, and bolts. That is the most common hardened-steel job there is, and reviewers consistently got the fastener out with this set.
There is a real limit though, and one buyer documented it on a Rockwell 55 test coupon. The set loses its edge on tool steel above mild steel hardness, which puts it below the M42 sets for genuinely hard material. It is also brittle in a handheld drill and behaves better in a press.
Why duplicate sizes matter for extraction work
Extraction is a numbers game. You will typically go up in steps from the fastener diameter, and the last step on a seized bolt is where the bit usually breaks. Having two of the 1/8 inch and two of the 3/16 inch in the case means a snapped bit is an inconvenience instead of an evening ending.
The 3-flat shank also matters here. On a drill-out you are pushing straight down with a lot of torque, and a round shank can slip in the chuck at exactly the wrong moment. Forum users doing this work consistently tell you to use a press if you can, which is the single most effective change you can make.
When to skip the WildBossy set
Skip it if your material is above mild steel hardness on the Rockwell C scale. For that range, the M42 sets at the top of this roundup hold an edge far longer, and above roughly 50 HRC you should be looking at a carbide-tipped bit instead.
The case is also lighter duty than ideal for a truck bed, and the set is inch-only.
9. toolant 21-Piece TiAlN Coated Cobalt Set – Best for Coated Heat Resistance
Pros
- Coating keeps edges sharp in heat-generating work
- Bullet point tip starts without a pilot hole
- Duplicates at the five smallest sizes
Cons
- 8% of reviews are one star
- Coated small bits can chip at the point on very hard steel
Best for coated heat resistance, because the titanium aluminum nitride coating raises surface hardness to 89 HRC and is built to hold an edge where the heat is. A cobalt body handles heat through its alloy; a coating handles it at the surface, which is where the temperature actually spikes during a cut.
Twenty-one pieces cover 1/16 inch to 1/2 inch with duplicates at the five smallest sizes. The bullet point tip is designed to be sharp and self-centering, reducing wandering without needing a pilot, and the 3-flat shank gives you grip in the chuck.
About 71% of buyers give five stars, and the credit goes to the coating and the point geometry for fast, accurate drilling in steel and stainless. The duplicate small sizes are a quietly good decision, since those are the bits that wear out first on hard material.
Roughly 8% of reviews are one star, the second-highest negative share in the group, and the reason is consistent: coated small bits can chip at the point on very hard steel. A chipped coating edge exposes the cobalt underneath, which is still good, but the geometry is now off.
Why a coating earns its place on long cuts
On a long cut through thick stock, most of the heat goes into the edge. A TiAlN coating has outstanding heat resistance, so the edge stays sharp longer than an uncoated cobalt bit of the same alloy. That is why coating sets are the right call for production work and the wrong call for a one-off job where you could simply buy a new bit.
There is a trade-off worth naming: a coating cannot be re-sharpened. Once the edge is gone, the bit is finished. The cobalt-bodied sets can go back on a grinder, which is why r/metalworking users describe cobalt as an investment rather than a consumable.
When to skip the toolant set
Skip it if you plan to re-sharpen your bits, since you would be grinding the coating away. Also skip it for very small diameters on the hardest steel, where point chipping is the most common complaint.
One more caution: coated bits and impact drivers are a debated combination. Use a driver for hex-shank bits designed for it, and stay with a chuck for this set.
10. Pro Edge Technology 20-Piece TiAlN Coated Set – Best for Chip Evacuation
Pros
- Coating extends service life over uncoated bits
- Double flute geometry moves chips in blind and through holes
- Duplicate bits at common sizes cut downtime
Cons
- 8% of reviews are one star
- 5% cobalt is a step below M42 sets on the hardest steel
Best for chip evacuation, and the double spiral flute is the reason. Rather than a conventional single-helix twist, this geometry is engineered to keep chips moving through and around the flutes in both blind and through holes. Fewer packed chips means less heat, less glaze, and a bit that keeps cutting at size.
Underneath the coating it is M35 high-speed steel with 5% cobalt, industrial-grade TiAlN coated to 70 HRC, with a bullet point tip for centering and higher feed. Twenty bits sit across 14 sizes from 1/16 inch to 1/2 inch, with extra pieces at the commonly used sizes.
The practical fit is a shop that already owns a good alloy set and keeps burning through a few sizes faster than it would like to replace them. A double flute that clears chips plus a coating that resists heat is a sensible pairing for anyone running several deep holes a week in stainless or alloy stock.
Why chip evacuation decides a lot of holes
A drill that cannot clear its own chips rubs instead of cuts, and rubbing generates the heat that kills a cobalt edge. A double flute geometry raises the feed you can sustain before the flutes pack, which on a deep hole in hard material is often the difference between one bit and three.
Around 70% of buyers give five stars, crediting the coating and bullet point with good life in stainless and alloy steel. A notable minority report early breakage on hardened material, and 8% of reviews are one star, tied for the highest negative share here.
When to skip the Pro Edge set
Skip it for the very hardest steel, because 5% cobalt sits a step below M42 for sustained heat on quenched material. If you already own an M42 set, this is a supplement for the sizes you go through quickly, not a replacement.
Also skip it if you intend to re-sharpen, since the coating will not survive a grinding wheel.
Cobalt vs Carbide: Which Material for Which Hardness
Hardness is measured on the Rockwell C scale, written as HRC, and it decides the whole question. Below roughly 30 HRC you are dealing with mild or medium carbon steel that plain high-speed steel handles fine. From about 30 to 45 HRC, cobalt alloy is the right tool. Above 45 HRC you need a carbide tip, and above 55 HRC a cobalt bit will glaze and burn almost immediately.
Cobalt is a heat-resistant material, not a hardness-resistant one. That distinction is the single most misunderstood point in this category, and it is repeated constantly in the forums. M35 is 5% cobalt and M42 is 8%, and the higher grade simply tolerates more heat before losing its edge. Neither one will cut a fully hardened tap, an easy-out, or a spring part at 60 HRC.
Carbide flips the trade-off. A carbide tip is harder than the workpiece, so it cuts hardened tool steel, but it is brittle and it will snap almost instantly if it is misaligned. That is why carbide wants a rigid machine, a short overhang, and a pilot step. The forums are blunt about this: carbide in a handheld drill on a hard part is a coin flip, and the fix is a press, not a better bit.
For a real hardened fastener, the honest answer is that a carbide-tipped bit in a drill press or a mill is the tool that works. Several users report never clearing an extractor with cobalt and finishing the job in a few minutes with solid carbide in a rigid setup. If the part cannot be removed or annealed, that is where the cost of carbide is justified.
How to Drill Hardened Steel Without Snapping a Bit
Technique decides more outcomes than the set you bought. The consensus across machinist forums converges on three rules: go slow, use lubricant, and let the machine’s weight supply steady feed pressure. Here is the sequence we use.
Pilot drill. Start a hole one-eighth inch under final diameter with a sharp cobalt or carbide bit. This is the step that stops the tip skating on a hard surface.
Set the speed. Slower than you think, and always with a firm, constant feed. On a handheld drill, the trigger setting matters more than the name on the chuck.
Add cutting fluid. Flood the hole every few seconds. Tapping wax and plain machine oil are the household substitutes and both work far better than a dry cut.
Peck rather than plunge. Pull the bit out every inch or so to clear chips, especially in a blind hole. Packed chips are the main cause of heat and glaze.
Back off to clear, not to cool. The goal of backing off is chip evacuation. Dwell on the bottom of a hole and you will glaze the tip.
Let the bit cool between holes. A red tip or a change in sound means stop.
For broken bolts and snapped taps specifically, step up in increments rather than attacking final diameter, and keep a spare of the current size on hand. The 20-piece and 21-piece sets with duplicate small sizes exist for exactly this reason.
Buying Checklist for Hardened Steel Drill Bit Sets
Before you buy, work through these criteria in order. Most disappointing purchases fail on the first one.
Alloy grade. M35 is 5% cobalt, M42 is 8%. For hardened material, buy M42 unless the set is a step budget option for mild work.
Size increments. Full 1/64 inch coverage from 1/16 to 1/2 inch is the useful standard. A set with gaps forces you to open a second hole.
Metric or inch. Metric sets are a genuine gap in an inch range. Buy the one matching your hardware and skip the other.
Tip geometry. A 135 degree split point, pilot point, or bullet point starts without walking. A 118 degree standard point will wander on hard stock.
Shank. A 3-flat or hex shank grips a chuck without slipping. Round shanks are fine in a three-jaw chuck and useless in a quick-change sleeve.
Length. Jobber length is standard and rigid. Stubby length is for access. Pick one set of each if you work in confined areas.
Coating. A TiAlN coating adds heat resistance but removes the ability to re-sharpen. It suits production cutting, not repair work.
Diameter ceiling. Anything above half inch needs a separate bit or a reduced-shank set with a larger chuck.
Case quality. A weak latch fails in a truck bed. Buyers complain about this more than almost anything else.
Duplicate sizes. If you break fasteners, extra pieces at the small sizes are worth more than two extra unique diameters.
One honest note on expectations: for ordinary stainless, alloy, and mild steel, a mid-tier named-brand set is usually fine, which is the view repeated in r/Machinists threads. The money only matters when you are working genuinely hardened material, and at that point a press matters more than the set.
Frequently Asked Questions
What type of drill bit is best for drilling through hardened steel?
For steel up to about 45 HRC, an M42 cobalt bit with a 135 degree split point is the right choice, because the 8% cobalt alloy survives the heat generated while cutting. Above 45 HRC, use a carbide-tipped bit in a drill press, since cobalt will glaze and burn. Always pilot drill, use cutting fluid, and feed steadily.
Is carbide or cobalt better for drilling hardened steel?
Cobalt wins below roughly 45 HRC because it is tough and forgiving in a handheld drill. Carbide wins above that because only a harder tip can cut quenched material, but it snaps instantly if misaligned. Rule of thumb: cobalt in the field, carbide in a rigid press, and a mill for the hardest 60 HRC work.
Will a cobalt drill bit drill hardened steel?
Partly. Cobalt resists heat, not hardness, so it works well on through-hardened bolts and alloy steel up to around 45 HRC. It will not touch a fully hardened tap, extractor, or a 60 HRC part, and a user on the r/Tools forum describes cobalt as fine unless you are drilling truly hardened material.
What drill speed is best for hardened steel?
Slower than instinct suggests, with firm constant feed. On a handheld drill, stay in the lower trigger range on small diameters and back the bit out every inch or so to clear chips. Heat, not speed, is what kills a cobalt edge, and a packed flute rubbing instead of cutting generates it fast.
What is better, M35 or M42 cobalt?
M35 is 5% cobalt and M42 is 8%. M42 holds an edge noticeably longer under sustained heat, so it is the better buy for hardened steel and production work. M35 is still a good alloy for stainless and alloy steel, and it costs less. The gap only shows up when the bit runs hot for more than a few seconds.
What are the best drill bits for removing broken bolts?
Step up in increments rather than drilling final diameter first, keep a spare of the current size, and use a counter-clockwise reverse bit to spin the fastener out once the hole is concentric. If the fastener is fully hardened, a carbide-tipped bit in a press or a mill is the realistic option, as forum users report cobalt rarely clears an easy-out.
Our Final Verdict on Hardened Steel Drill Bit Sets
The Bosch CO14B is the best of the best drill bit sets for hardened steel in 2026 because it combines the highest alloy grade in the group with a surface-hardened tip, and it carries the largest body of owner feedback of anything we tested. The IRWIN 29-piece set takes top marks for its 1/64 inch coverage, and the STROTON metric set is the one to buy if your hardware is metric.
What no set here will do is drill a fully hardened tap. For that job, a carbide-tipped bit in a press or a mill is the honest answer, and the forum consensus agrees. Pick the cobalt set that matches your sizes, pilot every hole, keep the lube coming, and your bits will last far longer than the last set you burned through.
There are people who love playing video games, and then there are enthusiasts who devote their lives to gaming.
Corey has been playing games since The Legend of Zelda and Final Fantasy III were still young.
Today, he blends his passion and experience to write reviews that can help others choose the best components in the gaming arena.