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Drilling through thick steel is a different beast than boring into wood or drywall. A standard bit heats up fast, dulls in seconds, and leaves you fighting a walk that ruins your center punch mark. You need a bit made from a harder alloy — M35 cobalt with a 135° split point (a tip geometry that starts cutting on contact instead of wandering) is the real spec to look for — and you need the right number of flutes and the right coating to clear the hot chips that pile up as you cut. This guide covers seven sets that actually handle the job, with the trade-offs each brings.
I’m Mohammad Maruf — the founder and writer behind Gardening Beyond. This guide is built by comparing the manufacturers’ published specifications and the patterns across verified customer reviews, so you get each pick’s real strengths and trade-offs instead of marketing spin.
Whether you are drilling through a truck frame or a steel bracket, the right set makes the difference between a clean hole and a broken bit. Here is what you need to know before picking the best drill bit for thick steel for your next project.
Quick Picks
- STROTON 5% Cobalt Drill Bit Set (21PCS) — Best Overall
- Narwhal 1/2 Inch Cobalt Drill Bits (3 Pack) — Premium Pick
- BECOLLO 11/32 Inch Cobalt Drill Bit Set (5-Piece) — Best Value
- WildBossy M35 Cobalt Drill Bit Set (20PCS) — Full Range Pick
- Yougfin 21PCS Cobalt Drill Bit Set — Solid Entry Set
- Cortool 3/8 inch Cobalt Drill Bits (6Pcs) — Budget Set
- RCINDUS 3/16″ Cobalt Drill Bit (20PCS) — Volume Pack
How To Choose The Best Drill Bit for Thick Steel
Picking the right bit for thick steel depends on a few key specs. Skip the shiny marketing claims and focus on what actually keeps the edge sharp and the hole clean.
Material: M35 Cobalt vs. Plain HSS
Standard high-speed steel (HSS) bits lose their edge fast when you push them through hardened steel or thick plate. For this job, look for M35 cobalt steel — it contains 5% cobalt, which makes the alloy harder and more heat-resistant. The result is a bit that stays sharp much longer and can handle the friction of cutting through stainless steel and cast iron without annealing the tip.
Point Angle: Why 135° Split Point Matters
A 135° split point is a small design change that makes a big difference. The sharper angle reduces the pressure you need to start a hole, and the split geometry cuts the web at the tip so the bit bites into the steel immediately instead of skating around. You often do not need to center-punch first because the bit self-centers. For thick steel, a split point is nearly essential — a standard 118° point will walk and make you fight the drill the whole way.
Flute Design and Coatings
A fully ground spiral flute clears the hot, sharp chips out of the hole as you drill. That reduces friction and heat buildup, which keeps the cutting edge cool. Some bits add a titanium or gold oxide coating for extra lubricity, but a well-ground flute in bare M35 cobalt often outperforms a coated plain HSS bit. For steel, you want a bit with a straight shank that fits tight in your chuck and a flute length long enough to clear the material thickness you are drilling.
Quick Comparison
| Model | Best For | Material | Size Range | Point Type | Amazon |
|---|---|---|---|---|---|
| STROTON 5% Cobalt 21PCS | High-volume work | M35 Cobalt (68 HRC) | 1/16″ – 3/8″ | 135° Split | Amazon |
| Narwhal 1/2″ 3-Pack | Large-diameter holes | M35 Cobalt | 1/2″ | 135° Split | Amazon |
| BECOLLO 11/32″ 5-Piece | Thick steel plate | Cobalt Steel | 11/32″ | 135° Split | Amazon |
| WildBossy M35 Cobalt 20PCS | Versatile kit with big bits | M35 Cobalt Steel | 1/16″ – 1/2″ | 135° Split | Amazon |
| Yougfin 21PCS | Entry-level cobalt set | M35 Cobalt HSS | 1/16″ – 3/8″ | 135° Split | Amazon |
| Cortool 3/8″ 6-Piece | Budget-friendly set | M35 HSS Cobalt | 3/8″ | 135° Split | Amazon |
| RCINDUS 3/16″ 20PCS | Small-bit volume pack | M35 Cobalt | 3/16″ | 135° Split | Amazon |
In‑Depth Reviews
1. STROTON 5% Cobalt Drill Bit Set (21PCS)
The set that survived 76 holes in heavy steel with almost no wear.
This is the pick for anyone who needs to drill a lot of holes without constantly swapping or sharpening bits. The M35 cobalt steel is rated at 68 HRC (Rockwell hardness scale — a measure of how hard the metal is), which makes it harder and more heat-resistant than standard HSS bits. You get 21 sizes from 1/16 inch up to 3/8 inch, all with a 135° split point and uncoated finish. The split point helps the bit self-center so you do not have to use a center punch every time, and the fully ground spiral flutes clear hot chips fast to reduce friction.
Buyers report excellent real-world performance. One owner noted that after a year of use, the bits still cut well enough to justify buying a second set. Another reviewer drilled 16 holes through 5/8-inch steel and 60 holes through 3/16-inch steel and saw almost no wear on the cutting edges, attributing the success to using a drill press at slower speed with cutting oil. The bits with diameters from 3/16 inch to 3/8 inch have a 3-flat shank (three flat sides where the chuck grips), which prevents spinning inside the drill.
Why it stands out
- 68 HRC hardness delivers long edge life in tough steel.
- 21 sizes cover from tiny pilot holes up to 3/8 inch.
- 3-flat shank on larger bits stops them from slipping in the chuck.
One thing to note
- The metal case is made from Q235 cold rolled steel, which is sturdy but adds weight compared to a plastic index case.
Lean into this if: you need a heavy-duty set for regular work on steel — this is the set that keeps cutting hole after hole.
Think twice if: you only need a few specific sizes and want to save shelf space; a smaller targeted set might suit you better.
2. Narwhal 1/2 Inch Cobalt Drill Bits (3 Pack)
A half-inch cobalt bit that ate through cast iron like plastic, owners mention.
When you need to drill a big hole, this three-pack of 1/2-inch M35 cobalt bits delivers the diameter most sets top out below. The bits have a flute length of 4 inches and a total length of 6 inches, giving you enough reach to go through thick material. Each bit is fully ground and uncoated with a 135° split point, which means the tip grabs the steel immediately rather than skating around. The heads are a full 32% more cutting diameter than a 3/8-inch bit, so you can open up larger passages in one pass rather than stepping up.
Customers note impressive results. One owner drilled 70-plus holes in thin stainless steel and reported the first bit was still sharp and unbroken after 80 holes. Another reviewer said the Narwhal bit absolutely ate through cast iron like it was plastic, calling it the best bit bought in 45 years. A third noted drilling through 3/8-inch thick steel at a 25-degree angle, emphasizing that using lubricant is key. The bits come in a plastic storage case for organization.
What makes it worth it
- 1/2-inch diameter handles large holes that typical kits skip.
- 6-inch overall length gives you depth for thicker materials.
- Buyers confirm it stays sharp for dozens of holes in tough metal.
Trade-off
- You only get three bits in one size — not a general-purpose set.
Reach for this if: you regularly drill 1/2-inch holes in cast iron, stainless, or thick steel and want industrial-grade longevity.
Look elsewhere if: you need a range of sizes for different jobs; this pack is a specialist, not a generalist.
3. BECOLLO 11/32 Inch Cobalt Drill Bit Set (5-Piece)
Drilled 11 holes through thick steel plate where a pricier competitor failed on one.
This five-pack of 11/32-inch cobalt bits punches far above its price tag. The bits are made from cobalt (5%) high-speed steel, with a fully ground surface and a 135° split point that prevents walking. The cutting diameter is 8.57 millimeters, which is roughly 80% wider than a 3/16-inch bit, letting you drill a solid mid-size hole in one shot. The set comes in a plastic case for storage, manufactured to ANSI B94-11M standards (a U.S. national standard for twist drill dimensions).
One reviewer noted these bits drilled 11 holes through thick steel plate using only three bits — after a competitor’s two bits failed on just one hole. Another reviewer used them to drill through leaf springs on an F150 truck — a notoriously hard steel — and noted you need to keep the RPM low and constantly oiled. A third reported that while they could not penetrate hardened steel, they worked fine on mild steel, calling them a good value for metalwork. The 135° split point tends to walk slightly on start, so buyers recommend using a center punch first.
Strengths at this price
- Comparable performance to higher-priced bits on thick plate steel.
- 5 bits per pack give you backups for the same size.
- ANSI-compliant manufacturing for consistent diameter.
Limitation
- Struggles with fully hardened steel — best for mild and medium-hard metals.
Grab for: drilling moderate-size holes in thick plate or structural steel without spending a lot.
Skip if: you need to drill through hardened or tool steel — this set is not designed for that.
4. WildBossy M35 Cobalt Drill Bit Set (20PCS)
A 20-piece kit with a 1/2-inch bit included for big jobs.
This set from WildBossy is one of the few kits that includes a 1/2-inch bit alongside smaller sizes from 1/16 inch upward, making it a true one-box solution for people who drill steel at different scales. The bits are M35 cobalt steel with a titanium surface coating (a thin, hard coating that reduces friction) and a 3-flat shank on the larger bits to prevent them spinning in the chuck. Each bit uses a 135° split point for self-centering, and the flutes are precision fully ground for smooth chip movement. The set holds 20 pieces, compared to the 21 pieces in some other kits, but it includes the valuable 1/2-inch size that many skip.
One reviewer described them as probably the best affordable drill bits on the internet, using them to drill out snapped taps and studs in turbo housings. Another reported that the bits went through thin stainless steel effectively, praising the two straight sides on the shank that keep the bit from spinning in the drill. One buyer mentioned that a few bits in the set were dull from the start and one snapped quickly, suggesting some quality variation between individual bits. The kit includes a plastic index case for storage.
Why this set works
- Includes a 1/2-inch bit — a size many kits leave out.
- Titanium coating adds extra lubricity for steel drilling.
- 3-flat shank on larger bits prevents chuck slipping.
Watch out for
- Some bits arrived dull or snapped on first use, per buyer reports.
Best for: someone who wants a broad range of sizes, including a half-inch bit, without buying separate sets.
Not ideal for: critical jobs where every bit must perform perfectly from the start — the quality seems to vary per piece.
5. Yougfin 21PCS Cobalt Drill Bit Set
A well-finished set that reviewers point out works especially well on stainless steel.
Yougfin’s cobalt M35 high-speed steel bits come with a gold oxide finish (a decorative surface treatment that also provides some corrosion resistance) and a 135° split point. The set includes 21 pieces ranging from 1/16 inch to 3/8 inch, with the classic jobber length (a medium-length drill bit that balances reach and rigidity for most metalworking tasks). The dual-flute design provides two cutting edges and two grooves that remove chips and allow cutting fluid to reach the cutting action. The bits have a straight shank that fits standard drill chucks.
Shoppers say that the bits are very sharp and long-lasting. One user who does a lot of construction work with steel in Montenegro noted that cobalt bits like these are essential for drilling through steel. Another reviewer said they work especially well on stainless steel, and the bits come in a really nice index case. One owner mentioned the case began to break apart after some use, which was the only downside noted. The cut speed was described as nice, and the variety of sizes was appreciated.
What buyers like
- Very sharp from the start and work well on stainless steel.
- 21 sizes cover most common drilling needs for shop and home.
- Gold oxide finish adds some protection against rust.
One buyer note
- The storage case is not very durable and may break apart with repeated use.
Good for: a first-time buyer of cobalt bits who wants a complete size range and sharp edges from the start.
Not great for: heavy construction work where the case will be tossed around — you may need a separate organizer.
6. Cortool 3/8 inch Cobalt Drill Bits (6Pcs)
Six identical 3/8-inch bits for bulk drilling and pilot holes at a low price.
This Cortool set earns its spot because it uses M35 cobalt (a harder alloy that stays sharp longer in thick steel than standard HSS) with a 135° split point that bites immediately instead of walking. You get six pieces of 3/8-inch M35 HSS cobalt bits with a cobalt added coating. Each bit has a cutting diameter of 0.38 inches, a flute length of 93 millimeters, and a total length of 128 millimeters — jobber length that fits most power drills currently on the market. The bits use a 135° split point with a straight shank and a fully ground spiral groove design that clears particles quickly. One owner reported using these bits in a mag drill and a milling machine, saying they cut great, last a long time, and that the 7/32 and 1/2 bits are equally good — but note that this set only contains 3/8-inch bits. If you need a range of sizes, this single-size set is not for you.
A buyer who rates them 4 out of 5 stars says: “They cant handle any steel even slightly hardened, but for normal metals it isnt a problem.” Another reviewer called them excellent value, noting that HSS-G (ground HSS) holds an edge longer than HSS-R (rolled HSS) while being less brittle than cobalt, though for steel drilling you want the cobalt content. The smaller bits in the set are prone to breaking, one owner warned — so skip this set if you need to drill hardened steel or rely on tiny diameters.
What works
- Six bits in the same size means you have plenty of backups.
- Works well in mag drills and milling machines per buyer reports.
- Very budget-friendly for a 6-pack of M35 bits.
Limitations
- Cannot handle hardened steel at all — normal metals only.
- Only one size (3/8 inch) — not a versatile set.
Pick these if: you need a handful of identical 3/8-inch bits for bulk drilling in mild steel and do not need a variety of sizes.
Skip if: you need to drill into hardened steel, cast iron, or any alloy with significant hardness.
7. RCINDUS 3/16″ Cobalt Drill Bit (20PCS)
Twenty 3/16-inch bits that outperformed a name-brand bit, buyers report.
If you burn through small bits quickly, this 20-pack of 3/16-inch M35 cobalt bits gives you a huge supply. The cutting diameter is 4.76 millimeters, and the bits use a 135° split point for self-centering to prevent walking on hard surfaces. The full grinding and hardening processes are done in the factory, and the diameter accuracy is controlled within -0.03 millimeters — a tight tolerance that ensures a consistent fit. The bits are uncoated, so you are getting the base M35 performance without any surface treatment.
Owners mention strong real-world performance. One customer observed a single bit from this set outperformed a Milwaukee bit, drilling around 25 stripped screw heads before dulling — a great result for extracting countersunk screws from wood decking. Another owner needed to drill holes through a 1/8-inch steel plate and used one bit for all 10 holes, noting it drilled as well on the last hole as it did on the first. One buyer called them good quality low cost jobber drill bits and said they worked great for pre-drilling deck screws. The bits come in a plastic storage case.
The upside
- 20 bits for the price of a few name-brand bits — great value.
- One bit handled 10 holes in 1/8-inch steel plate with no wear.
- Tight diameter tolerance (-0.03 mm) for consistent drilling.
The catch
- Only available in 3/16-inch — limited to small-hole work.
Ideal for: anyone who needs a large quantity of small cobalt bits for repetitive drilling in mild steel, stainless, or for screw extraction.
Not the set for: drilling large holes or working with hardened tool steel — stick to the larger diameter sets above for that.
Understanding the Specs
M35 Cobalt vs. HSS
M35 is a specific grade of high-speed steel that contains 5% cobalt. The cobalt makes the steel harder and more heat-resistant, so the bit retains its sharp edge much longer when drilling through thick steel, stainless steel, or cast iron. Standard HSS (without cobalt) softens faster under the friction of metal drilling. M35 is the baseline to look for in any bit meant for thick steel.
135° Split Point
A 135° split point is a tip geometry where the cutting edge is ground with a split that runs across the web (the central thickness of the bit). This design lets the bit start cutting immediately without walking or wandering across the surface, so you often do not need a center punch. The 135° angle also reduces the pressure required to begin drilling, which is a real help when you are working with a hand drill against tough steel.
Jobber Length
Jobber length is the standard flute-to-shank proportion for general-purpose metal drilling bits. A jobber bit is long enough to reach through moderate material thickness and clear chips effectively, but it is shorter than an aircraft or extended-length bit, giving it better rigidity. For drilling thick steel, jobber length is the right balance — stiff enough to resist bending, long enough to go through 1/4-inch to 1/2-inch plate.
3-Flat Shank
Some larger bits (typically 3/16 inch and up) have three flat sides ground onto the round shank. These flats give the chuck jaws more grip than a smooth round shank, preventing the bit from spinning inside the drill under heavy torque. If you have ever had a drill chuck loosen mid-hole and the bit stop cutting, a 3-flat shank is the fix.
FAQ
Can I use these cobalt bits in a hand drill or do I need a drill press?
Do I need to use cutting oil with these bits?
Will a 135° split point bit work without a center punch?
How do I know what speed to run my drill for steel?
What is the difference between M35 and M42 cobalt bits?
Can cobalt drill bits be sharpened?
Will these bits work on hardened steel or springs?
How many holes should I expect from one bit in thick steel?
What is a jobber length bit and why does it matter for steel?
Are titanium-coated bits better than uncoated cobalt bits for steel?
Final Thoughts: The Verdict
Across the board, the best drill bit for thick steel is the STROTON 5% Cobalt 21-piece set because of its proven longevity — one set survived 76 holes in heavy steel with almost no wear. If you want a premium 1/2-inch bit for the biggest jobs, grab the Narwhal 3-pack. And for a budget-friendly entry into cobalt bits that still handles thick plate steel effectively, the BECOLLO 11/32-inch 5-pack is the smart choice.
How We Picked
We do not accept paid placement. Every pick is matched to a real buyer and a real use-case; we do not hands-on test units.
Sources & Methodology
Specifications: manufacturer listings and product documentation. Review insights: verified customer reviews, as of July 2026. Pricing: not shown on this page (it changes often); check the current price via the retailer link.
As an Amazon Associate, Gardening Beyond earns from qualifying purchases. This does not affect which products we feature.