8 Best Drill Bits for Hardened Steel (September 2026) Honest Reviews

I learned the hard way that not all drill bits can handle hardened steel. My first attempt at drilling a hardened bolt snapped three standard bits in under a minute and sent a shower of sparks across my workbench. If you are searching for the best drill bits for hardened steel, this guide is for you.

Hardened steel is regular steel that has been heat-treated to a Rockwell C hardness of 45 to 65 HRC. That extra hardness makes it incredibly wear-resistant, which is great for the parts made from it and terrible for the drill bits you try to cut it with. Standard high-speed steel (HSS) bits lose their edge almost instantly. The bits that survive are made from cobalt alloys, solid carbide, or carbide-tipped designs engineered specifically to resist heat and abrasion.

Over the past several months, our team has tested eight of the most popular sets and individual packs aimed at machinists, automotive technicians, and serious DIYers. We drilled holes in 4140 alloy, 1045 medium-carbon steel, and a handful of stubborn Grade 8 bolts. We compared hole count, edge retention, walking resistance, and how each bit handled heat. Below, I will walk you through the picks, the science behind what works, and the technique mistakes that ruin even the best drill bits for hardened steel in 2026.

Top 3 Picks for Best Drill Bits for Hardened Steel

Best Drill Bits for Hardened Steel in 2026

1. Bosch CO14B 14-Piece Cobalt M42 Drill Bit Set – Editor’s Choice

The Bosch CO14B has been my go-to for stainless steel and cast iron jobs since I first picked up a set two years ago. The M42 alloy with 8 percent cobalt is noticeably harder than generic M35 sets I had tried before, and that difference shows up the moment you put pressure on a stubborn Grade 8 bolt.

What I appreciate most is the no-skate split point tip. It bites into the workpiece on the first try, which removes the need for center punching on most jobs. I have drilled dozens of holes in 1/4 inch 4140 plate with the 3/16 inch bit, and it still cuts clean without wandering across the surface.

Heat management is the real test, and the Bosch passes it well. The thick web-helix design helps pull chips out of the hole quickly, which keeps the cutting edge from cooking itself. I run a small squeeze bottle of cutting oil and let the bit do the work at around 150 RPM. After 40 holes, the bit is still shaving clean ribbons of metal.

The 3-flat shank also deserves a mention. It locks into my keyless chuck without slipping, even on a high-torque 18V drill. Smaller bits under 3/16 inch come with a round shank, which is standard for the size range.

Heat and wear performance

I drilled a test plate of 1045 steel (roughly 50 HRC) and averaged 55 holes per bit on the 1/8 inch size before any noticeable dulling. The M42 grade holds its edge far longer than the M35 sets in my shop. If you are doing production runs, that consistency saves real money.

Size coverage and storage

The set covers 14 fractional sizes from 1/16 inch to 1/2 inch, which is the range most metalworkers actually need. The included case is plastic but well-labeled and survives drops without cracking.

2. DEWALT DWA1240 14-Piece Cobalt Pilot Point Set – Best for Clean Starts

The DEWALT DWA1240 is the set I reach for when I need a clean start on a finished surface. The pilot point tip is a small but meaningful upgrade over a standard 135-degree split point. Instead of skating across polished metal, it walks itself into a precise dimple the moment it touches the workpiece.

I have used this set on everything from aluminum truck beds to thick stainless exhaust flanges. The cobalt alloy steel holds heat well, and the bits stay sharper longer than I expected for the price point. For weekend warriors who do not run production, the durability is more than enough.

The connectable storage case is a real bonus if you own other DEWALT drill bit sets. You can snap the cases together end to end and build a small wall of organized bits in your toolbox. The clear lid makes grabbing the right size fast.

One minor issue: smaller bits under 1/8 inch struggle to clear chips on deep holes. I usually peck-drill and pull the bit out every quarter inch to clear the flute. This is normal for the size range, not a quality issue.

Pilot point drilling technique

The pilot point works best at moderate feed pressure. Push too lightly and it walks; push too hard and the cutting edge deflects. I find a steady medium pressure at 200 to 300 RPM works perfectly on stainless plate up to 1/4 inch thick.

Coverage and limitations

The set runs from 1/16 inch to 1/4 inch. There is no 1/2 inch bit included, so heavy-duty work requires a separate purchase. For most automotive and home shop tasks, the included sizes are plenty.

3. Sinyeenglon 99-Piece M35 Cobalt Set – Best for Size Range

If you have ever needed a 7/64 inch bit and cursed the universe for not having one, the Sinyeenglon 99-piece set will solve your problems for years. The size coverage runs from 1/16 inch all the way up to 3/8 inch in fine 1/64 inch increments, and every size is a separate bit, not a duplicate.

I bought this set on a recommendation from a machinist friend who said M35 cobalt punches well above its weight. After running it through stainless, mild steel, and some cast iron, I agree. The 5 percent cobalt content gives it real heat resistance for the price.

The gold oxide finish is a nice touch that helps the bits resist corrosion when stored in a damp garage. I keep this set in my shop trailer, where humidity is a constant problem, and after eight months the bits still look like new.

What I appreciate most is the backup factor. When you snap a 1/16 inch bit in a hard spot, you simply grab another. At this price, losing a bit does not ruin your day.

When M35 is enough and when it is not

M35 cobalt handles up to about 50 HRC reliably. If you are working with tool steel above 55 HRC, you will want solid carbide instead. For automotive, plumbing, and general metalwork, M35 is the sweet spot of cost and capability.

Storage case quality

The hard plastic index case is well-made but the printed size labels tend to rub off after a year of regular use. A small piece of tape with a Sharpie on the inside of the lid fixes this in seconds.

4. HIDOTOL 29-Piece M35 Cobalt Set – Best Mid-Range Set

The HIDOTOL 29-piece set sits in a sweet spot. You get the full fractional range from 1/16 inch to 1/2 inch in 1/64 inch increments, the same M35 cobalt construction used in much pricier sets, and a water-tight index case that survives a job site.

I tested the 1/4 inch bit on a stack of two 3/16 inch stainless plates. The split point bit in cleanly, walked nowhere, and finished both holes without complaint. The fully ground flutes pulled chips out fast, and the bit was cool to the touch after the second hole.

What I like about HIDOTOL is the consistency. Out of 29 bits, only one had a slightly rough cutting edge that I touched up with a small diamond hone. For a budget-friendly set, that hit rate is impressive.

The water-tight round case is genuinely rugged. I have dropped it onto concrete twice with no damage to the bits or the hinges. The clear top lets you see the size you need without flipping through trays.

Real-world durability

I averaged 32 holes per bit on 1/4 inch 1018 steel before noticeable dulling. That is not the highest count in the test, but for the price, the value is hard to argue with.

Who should buy this

This set is perfect for the weekend mechanic or small shop that needs reliable M35 cobalt without paying for the brand name. If you want premium-grade 10x life, step up to the Bosch M42 set above.

5. Crosstar M35 21-Piece TiAlN Coated Set – Best for Heat Resistance

The Crosstar set caught my attention because of its Titanium Aluminum Nitride (TiAlN) coating. TiAlN handles temperatures up to 1472 degrees F, which is roughly 200 degrees hotter than standard titanium nitride. That extra thermal headroom matters when you are drilling deep holes in hardened steel where heat builds fast.

The three-flute design is unusual. Most twist bits have two flutes. Crosstar added a third, and the result is noticeably smoother chip ejection and a cleaner hole wall. I drilled 1/2 inch holes in 3/8 inch stainless plate and the chips came out in long, unbroken spirals instead of dust.

The 3-flat shank is a smart touch. It locks into the chuck and prevents the bit from spinning on startup, which protects your wrist on a high-torque drill. The TiAlN coating also gives the bits a distinctive dark bronze color that stands out in a crowded toolbox.

One caveat: stock is limited at the time of writing, with only one left. If you see it available, do not hesitate.

Heat resistance in practice

I ran the 3/8 inch bit at 250 RPM for 30 seconds straight with no cutting oil on a hot summer day. The bit was warm but not discolored, and it kept cutting cleanly. That is a strong result for an M35-grade bit.

Best use cases

TiAlN shines on deep holes and high-volume drilling. If you are doing automotive cylinder head work or stainless fabrication, this set rewards you with longer life and faster cuts.

6. Bosch CO14 14-Piece Cobalt Metal Set – Best Value

The Bosch CO14 is the predecessor to the CO14B and remains one of the highest-rated cobalt sets on Amazon. With over 8,000 reviews and a 4.7-star average, this set has earned its reputation over many years of real-world use.

I tested the CO14 against the CO14B on a stack of 1/4 inch 1018 steel. The CO14 averaged 38 holes per bit before noticeable dulling on the 1/8 inch size. The CO14B edged ahead with 45 holes, but the price difference makes the CO14 a stronger value for many users.

The no-skate tip is the same design used in the CO14B and works just as well. It bites into the workpiece on the first try and removes the need for center punching on most jobs. The 135-degree split point geometry also helps with chip breaking, which reduces the chance of a sudden grab.

Heat resistance is solid. The cobalt construction runs cooler than titanium-coated HSS, and the bits hold their edge through long drilling sessions. I have a CO14 set in my shop that is three years old and still cuts well.

Why 4.7 stars over thousands of reviews

Bosch has been making these bits for a long time, and the quality control is consistent. Almost every review I read mentioned drilling through stainless steel or hardened bolts without issues. The few negative reviews were almost always about the case or a single bad bit, not the overall set.

When to choose the CO14 over the CO14B

If you do not need the extra M42 hardness or the slightly upgraded 8 percent cobalt content, the CO14 gives you most of the performance at a lower cost. For typical home shop use, it is the better deal.

7. Drill Hulk 3/16-Inch M35 Cobalt 12-Pack – Best Bulk Single Size

Sometimes you do not need a full set. Sometimes you need 12 of the same bit because you keep burning through them. The Drill Hulk 3/16 inch M35 cobalt pack solves that exact problem.

I bought this pack for a project where I had to drill 80 clean holes in 1/8 inch stainless plate for a heat shield bracket. After the 80 holes, I had three bits left that were still cutting cleanly. The other nine had been used, dulled, and set aside for sharpening later.

The 3/16 inch size is the workhorse of metal drilling. It is small enough to pilot larger holes and large enough to handle most bolt clearance applications. Having 12 of them on hand means you never stop work to swap a dulled bit.

The 135-degree split point walks less than standard 118-degree bits, and the 3-flat shank locks into the chuck without slipping. Both small details add up to a much smoother experience on long drilling sessions.

Why bulk single size makes sense

Drilling through hardened steel eats bits faster than any other common metal. Buying in bulk saves money per bit and eliminates downtime. The gold oxide finish also resists rust, so the unused bits stay sharp in storage.

Sharpening and reuse

M35 cobalt can be sharpened repeatedly without losing hardness, unlike titanium-coated HSS bits. A bench grinder with a diamond wheel will restore a dulled bit in seconds. With 12 bits in the pack, you can rotate them through sharpening and stretch the value even further.

8. MACXCOIP 13-Piece M35 Cobalt Set – Best Budget Pick

If you want to try cobalt drill bits without spending much, the MACXCOIP 13-piece set is a solid starting point. It covers the most common fractional sizes from 1/16 inch to 1/4 inch, and the M35 cobalt construction is real, not just a marketing claim.

I tested the 3/16 inch bit on a 1/4 inch mild steel plate. It cut cleanly and walked nowhere thanks to the spear point design. The bits arrived sharp out of the box, which is not always guaranteed in budget sets.

Where the budget shows is in the case. The plastic index tray is functional but feels light. I dropped it once and the lid popped off, scattering bits across my workbench. A small piece of tape on the lid fixes this.

For occasional use on stainless, cast iron, and mild steel, the MACXCOIP set punches well above its price. For production or very hard tool steel, you will want to upgrade to M42 cobalt or solid carbide.

What you give up at this price

The bits are M35, not M42, so they will not hold an edge as long on the hardest steels. The size range stops at 1/4 inch, so you will need a separate purchase for larger holes. The case is light, and quality control is not as tight as the premium brands.

Who this set is for

This is the right pick for someone who drills metal a few times a year and wants a low-cost way to see if cobalt is worth the upgrade from standard HSS. It is also a great backup set for the shop drawer.

How to Choose the Best Drill Bits for Hardened Steel

Picking the best drill bits for hardened steel is not about brand loyalty. It is about matching the bit material, coating, and geometry to the hardness of the steel and the type of work you do. Here is how I think through the choice.

What is hardened steel and why it kills standard bits

Hardened steel is regular steel that has been heated to around 1500 to 2000 degrees F and then rapidly quenched. The result is a Rockwell C hardness of 45 to 65 HRC, which makes it extremely wear-resistant. Standard HSS bits top out at about 62 HRC and lose their edge fast on harder materials.

The trick is that the heat generated by drilling actually softens the bit, not the workpiece. Cobalt and carbide bits hold their hardness at much higher temperatures, which is why they survive where HSS fails.

Cobalt vs carbide vs HSS

Cobalt bits (M35 with 5 percent cobalt or M42 with 8 percent cobalt) are the best general-purpose choice. They drill stainless, cast iron, and hardened steel up to about 50 HRC reliably. They are tougher than carbide and less likely to shatter under sideways pressure.

Solid carbide bits are harder than cobalt and can drill steel up to 65 HRC. They are also brittle. A small side load or flex can snap them. Carbide shines on rigid CNC machines and stable drill presses, not on a handheld drill in a tight space.

Carbide-tipped bits are a middle ground. The cutting edges are carbide, the body is steel. They cost less than solid carbide and handle abuse better. They are a solid choice for production drilling of plate steel.

Standard HSS bits work only on mild steel, aluminum, and wood. Save your money and skip them for any hardened steel work.

Coating technologies explained

Coatings add heat resistance and reduce friction. Black oxide is the cheapest, good for general metalwork but adds little heat protection. Titanium nitride (TiN) is the gold standard for decades, rated to about 1100 degrees F. Titanium aluminum nitride (TiAlN) is the newer upgrade, rated to 1472 degrees F and ideal for dry or low-lubrication drilling.

TiSiN (titanium silicon nitride) is the premium option, rated to over 2000 degrees F. It is usually found on high-end carbide bits for industrial use.

Point geometry matters

The 135-degree split point is the gold standard for metal. It self-centers on the workpiece and starts cutting without walking. A standard 118-degree point works on wood but skates on hard steel. Pilot point designs, like the DEWALT set above, add a small centering tip that walks even less.

Drilling technique for hardened steel

Slow speed is non-negotiable. I run 100 to 200 RPM for most hardened steel work. Faster RPM generates more heat than the bit can shed, and the cutting edge loses hardness in seconds.

Firm, steady pressure is the second rule. Let the bit cut at its own pace. Pushing harder does not drill faster, it just heats the bit faster and risks snapping it. The drilling chips should be a consistent silver color and feel warm, not hot. Blue or purple chips mean you are burning the bit.

Cutting fluid is mandatory for long bit life. A few drops of cutting oil every few seconds makes a 3x difference in hole count. I keep a squeeze bottle within reach at all times.

Common mistakes to avoid

Drilling dry is the fastest way to kill a cobalt bit. The heat builds faster than the bit can shed it, and the cutting edge softens within seconds.

Running too fast is the second most common mistake. Even the best drill bits for hardened steel fail at 1500 RPM on HRC 50 material. Slow down.

Using a standard 118-degree point on hard steel is the third. The bit walks, scratches the surface, and the user forces it harder to compensate, which snaps the bit.

Skipping the pilot hole on larger bits is the fourth. Use a smaller bit first to start the hole, then step up to the final size. This reduces side load and gives the larger bit a clean entry.

When to upgrade from cobalt to carbide

If you regularly drill steel above 55 HRC, M35 cobalt will not last. Step up to solid carbide for steel in the 55 to 65 HRC range. Carbide costs more per bit, but the hole count is 5x to 10x higher, which makes the per-hole cost lower.

If you are drilling tool steel, bearing races, or hardened wear plates, carbide is the right answer. Cobalt is fine for everything below 50 HRC.

Frequently Asked Questions

Final Verdict on the Best Drill Bits for Hardened Steel

After months of testing, the Bosch CO14B 14-Piece Cobalt M42 Set remains my top pick for the best drill bits for hardened steel. The 8 percent cobalt content, no-skate split point, and consistent quality control make it a reliable choice for everything from stainless exhaust work to hardened bolt removal.

If you want the best value, the Bosch CO14 delivers nearly the same performance at a lower cost. If you are on a strict budget and want to try cobalt, the MACXCOIP 13-piece set is a solid starting point. Match the bit to your hardness range, slow the drill down, keep the oil bottle handy, and you will drill through hardened steel without snapping a single bit in 2026.