Drilling into hardened steel is one of the toughest tasks you can throw at a drill bit. Standard high-speed steel bits dull instantly, overheat, and snap when they meet a hardened surface, leaving you with a ruined workpiece and a wasted afternoon. The right bit, however, cuts cleanly, self-centers, and survives the friction without losing its edge.
I’m Rikta — the co-founder and writer behind FitlyFast. I’ve spent hundreds of hours analyzing drill bit metallurgy, point geometry, and real-world test data to separate the bits that actually handle hardened steel from the ones that just claim to.
This guide breaks down the best options for drilling into tough alloys, from budget-friendly cobalt sets to premium aerospace-grade steel. Whether you’re a machinist, a fabricator, or a serious DIYer, you’ll find the bits for drilling hardened steel that match your job and your budget.
How To Choose The Best Bits For Drilling Hardened Steel
Not all drill bits labeled “for metal” are built for hardened steel. The alloy composition, point geometry, and coating define whether a bit will chew through a hardened surface or simply spin in place and overheat. Focus on these three factors to make the right choice.
Material: Cobalt Content Is King
Standard HSS bits lack the hardness to cut through hardened steel, which typically measures between 45 and 65 on the Rockwell C scale. Bits made from M35 high-speed steel with 5% cobalt or M42 with 8% cobalt retain their edge at higher temperatures, resist deformation, and can handle the friction generated by drilling into tough alloys. Cobalt content is the single most important spec to check.
Point Geometry: 135° Split Point Is Non-Negotiable
Hardened steel is slick, and a standard 118° point will skate across the surface before it bites. A 135° split point creates two cutting edges that self-center, reduce walking, and start the hole exactly where you place the bit. This geometry also reduces the axial force required to penetrate, which means less drill motor strain and a cleaner hole.
Cutting Speed and Lubrication
Even the best bit will fail if you run it too fast or dry. Hardened steel requires slow spindle speeds — typically 300 to 600 RPM for a 1/8-inch bit, dropping lower for larger diameters — and constant application of cutting oil or paste to dissipate heat. Without lubrication, the bit edge will temper and dull almost immediately. Budget-friendly or premium, every bit in this guide demands the same careful drilling technique to deliver its full lifespan.
Quick Comparison
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| Model | Category | Best For | Key Spec | Amazon |
|---|---|---|---|---|
| Norseman 44170 | Premium HSS | Aerospace-grade durability | M2/M7 HSS, NAS 907B spec | Amazon |
| CaRoller 115-Piece Cobalt | Premium Cobalt | All-in-one professional set | 5% Cobalt M35, 135° split point | Amazon |
| WildBossy M35 20-Piece | Mid-Range Cobalt | Daily shop use on hard alloys | 5% Cobalt, 3-flat shank | Amazon |
| MACXCOIP Metric 19-Piece | Mid-Range Cobalt | Metric sizing for precision work | 1.0mm–10.0mm M35 cobalt | Amazon |
| CaRoller 29-Piece Black & Gold | Premium HSS | General metal drilling, value variety | W4 HSS, black oxide finish | Amazon |
| RCINDUS 3/16″ Cobalt 20-Piece | Budget Cobalt | Bulk supply for stripped screws | M35 5% cobalt, 135° split point | Amazon |
| DelitonGude 13-Piece Cobalt | Budget Cobalt | Entry-level hardened steel drilling | M35 5% cobalt, nitrided finish | Amazon |
In‑Depth Reviews
1. Norseman Drill Bits 44170 Ultra Dex Type 240-UB
The Norseman 44170 is the benchmark for premium high-speed steel drill bits. Made from specialized hi-molybdenum M2/M7 tool steel with a gold oxide finish, it meets the NAS 907B aerospace standard — a spec that demands consistent performance under extreme conditions. The 135° split point is precision ground, and the flutes, body, and clearance are all ground to tight tolerances, which translates to holes that are round, clean, and on-size every time.
Real-world testing confirms its toughness: one bit drilled over 100 half-inch holes in quarter-inch steel plate and remained sharp enough for further use. The set includes 29 fractional sizes from 1/16 to 1/2 inch by 64ths, covering virtually every common drilling need. This is not a cobalt set, but the M7 steel alloy delivers hardness comparable to low-end cobalt bits while offering better toughness and chip resistance.
The Norseman set is the choice for machinists and fabricators who cannot afford a bit failure mid-job. If you drill hardened steel regularly, this set will pay for itself inside a year.
Why it’s great
- Aerospace-grade construction ensures consistent, repeatable drilling
- One bit drilled 100+ holes in steel and stayed usable
- Made in the USA with precision-ground geometry
Good to know
- Premium price point — not a budget buy
- No cobalt formulation; M7 HSS is a different approach
- Gold oxide coating wears on aluminum, but holds cutting fluid on steel
2. CaRoller Cobalt Drill Bit Set 115 PCS
The CaRoller 115-piece set is the most comprehensive cobalt drill bit kit on this list, covering fractional sizes (1/16 to 1/2 inch by 64ths), letter sizes (A to Z), and wire gauge sizes (#1 to #60). Every bit is made from M35 high-speed steel with 5% cobalt, ensuring the heat resistance and edge retention needed for hardened steel. The 135° split point is present on every bit, preventing walking and reducing the chance of breakage.
In practice, the 5% cobalt formulation delivers consistent performance on stainless steel, cast iron, and hardened alloys. A single bit drilled 30 holes in a steel I-beam before showing significant wear — impressive for a set at this price per bit. The metal index storage box is rugged enough for job-site use and includes a built-in clip for belt carry, which solves the common problem of losing small bits in a toolbox.
For professionals and serious DIYers who need every size from #60 to 1/2 inch, this set eliminates the need to buy multiple kits. The per-bit cost is fraction of buying individual bits, and the cobalt composition means you are not sacrificing performance for quantity. If you need one kit to handle hardened steel across a wide range of hole sizes, this is the most complete option.
Why it’s great
- 115 bits cover fractional, letter, and wire gauge sizes
- Rugged metal case with belt clip prevents loss
- Consistent M35 cobalt performance across every bit
Good to know
- Some users report slight chipping on edges after heavy use
- Bits require slow speed and cutting oil to reach full lifespan
- Storage case is metal but not fully gasket-sealed
3. WildBossy M35 Cobalt Drill Bit Set 20PCS
The WildBossy M35 set strikes a strong balance between price and performance for daily shop use. The 20-piece fractional set ranges from 1/16 to 1/2 inch, with duplicates of the most-used smaller sizes — a practical feature when you inevitably break a 1/8-inch bit mid-job. The bits are made from M35 cobalt steel, rated to 67 Rockwell hardness, and the manufacturer claims they last up to 12 times longer than standard HSS bits.
A standout detail is the 3-flat shank design, which prevents the bit from spinning in the drill chuck under high torque. This is a real advantage when drilling hardened steel, where the cutting forces can twist a round-shank bit loose. The titanium surface coating adds a layer of lubricity that reduces friction and heat buildup, though it will wear off over time on very hard surfaces.
Reviewers consistently report that these bits drill through stainless steel and snapped-off taps with surprising ease when used at the correct slow speed with cutting oil. Some bits in the set arrived slightly dull, which suggests quality control is not perfect, but the overall value for a mid-range cobalt set is excellent. For the home machinist or the shop that needs a reliable backup set, this is a solid pick.
Why it’s great
- 3-flat shank prevents chuck slippage under heavy load
- Covers 1/16 to 1/2 inch with size duplicates for common diameters
- Ti coating reduces friction on initial cuts
Good to know
- Quality control inconsistency — some bits arrive dull
- Ti coating is thin and wears off on hard alloys
- Plastic storage case is functional but not job-site tough
4. MACXCOIP Metric 19Pcs M35 Cobalt Drill Bit Set
The MACXCOIP metric set fills a specific but important gap: fractional-inch bits do not always match the hole sizes required for metric fasteners, threaded inserts, or European-manufactured equipment. This 19-piece set includes sizes from 1.0mm to 10.0mm in 0.5mm increments, giving you precise control over hole diameter without having to step up to the next fractional size and ream.
Each bit is M35 cobalt steel with a 135° split point, and the full-grind construction ensures the flutes are smooth and the diameter is accurate to spec. Former CNC machinists in the reviews confirm these bits match the quality of industrial cobalt drills they used in production environments. The metal index box is compact enough to fit in shallow tool chest drawers, and the size markings on the case are clear and easy to read.
One note: the smaller bits — especially the 1.0mm and 1.5mm — are thin and require careful handling to avoid snapping. This is true of any small-diameter cobalt bit, but it is worth emphasizing if you plan to use the smaller sizes on hardened steel. For metric-focused shops or anyone who regularly works with European hardware, this set provides the precision that fractional sets cannot match.
Why it’s great
- Precise metric sizing from 1.0mm to 10.0mm in 0.5mm steps
- Compact metal case fits in shallow tool drawers
- M35 cobalt with 135° split point for hard alloys
Good to know
- Small bits (1.0mm–2.0mm) are fragile on hardened steel
- No duplicate sizes — break a bit and you lose that diameter
- Shank material softer than premium industrial bits
5. CaRoller 29Pcs Drill Bit Set, Black and Gold
The CaRoller 29-piece set stands out for its size range — it includes every 64th from 1/16 to 1/2 inch, which is 29 unique sizes. That level of granularity means you can drill a pilot hole and then step up to the exact final diameter without guessing or forcing an undersized bit. The bits are made from W4 high-speed steel with a black oxide finish and an amber coating, which provides corrosion resistance and some lubricity.
On mild steel and aluminum, these bits cut aggressively and cleanly. On stainless and hardened steel, they perform adequately when used with cutting oil and a slow drill speed — a user drilled 30 holes in a steel I-beam with a single bit before it began to dull. The 135° split point is consistent across all sizes, and the straight round shanks fit standard chucks without slipping.
These are not cobalt bits, so they will not match the heat resistance of M35 or M42 formulations on very hard alloys. For general metal drilling that occasionally includes hardened steel, however, this set offers the best size variety at a mid-range price. The plastic case is expandable and well-organized, making it easy to grab the exact bit you need without sorting through a pile.
Why it’s great
- 29 fractional sizes in 1/64th increments — maximum variety
- Black oxide finish reduces friction on initial cuts
- Good performance on mild steel and aluminum
Good to know
- Not cobalt — lacks heat resistance for sustained hard steel drilling
- Will dull faster than cobalt bits on stainless and hardened alloys
- Amber coating wears off quickly on abrasive materials
6. RCINDUS 3/16″ Cobalt Drill Bit 20PCS
The RCINDUS set is a single-size bulk pack — 20 identical 3/16-inch M35 cobalt bits. This is a niche product for a specific scenario: if you regularly drill 3/16-inch holes in hardened steel, stainless, or need to extract stripped screws, this pack gives you a consumable supply at a per-bit cost that is hard to beat. Each bit is made from M35 high-speed steel with 5% cobalt and a 135° split point.
Users report that a single bit can drill around 25 stripped screw heads before dulling, and the bits performed well on 1/8-inch steel plate, drilling multiple holes without losing sharpness. The plastic storage case keeps the bits organized and prevents them from rattling together and dulling each other. The diameter accuracy is rated within -0.03mm, which is tight enough for most standard applications.
The obvious trade-off is the lack of size variety — you get 3/16-inch or nothing. This set is best suited for professionals who go through a specific bit size quickly, or for DIYers who need a cheap, plentiful supply for demolition work. If you need a range of sizes, look elsewhere, but for sheer value per bit in a single diameter, this is the most cost-effective option on the list.
Why it’s great
- Extremely low per-bit cost for a single common size
- 20 identical bits in one pack — ideal for consumable use
- M35 cobalt handles hardened steel and stripped screws well
Good to know
- Only one size (3/16-inch) — no variety
- Plastic case is basic, not job-site rugged
- Small size limits use to lighter drilling applications
7. DelitonGude 13Pcs Cobalt Twist Drill Bit Set
The DelitonGude 13-piece set is the most affordable entry point into cobalt bits for hardened steel. It includes sizes from 1/16 to 1/4 inch in imperial fractions, giving you the most commonly used diameters for small to medium holes. Each bit is made from M35 high-speed steel with 5% cobalt, and a full-grinding nitriding process adds surface hardness and wear resistance.
User reports are mixed but generally positive at this price level. The bits drilled bronze and metal studs successfully when used with cutting oil and slow speed, outperforming titanium-coated HSS bits that failed on the same material. One reviewer noted that the 13/64-inch bit struggled on T-posts with 80+ Rockwell hardness, but the seller offered a full refund — good customer service for a budget product.
For the DIYer who wants to drill an occasional hole in hardened steel without investing in a premium set, these bits deliver acceptable performance. The nitrided finish helps the initial cut stay sharp, but the bits will dull faster than more expensive cobalt sets on sustained hard steel drilling. Consider this a trial set to see if cobalt bits work for your workflow before investing in a larger premium set.
Why it’s great
- Lowest-cost entry into 5% cobalt bits for hardened steel
- 13-piece set covers 1/16 to 1/4 inch in common sizes
- Manufacturer responsive to defects and complaints
Good to know
- Struggles on very hard surfaces (80+ Rockwell)
- Smaller bits prone to breaking under high torque
- Nitrided finish wears off faster than titanium coating
FAQ
Why do cobalt bits work better on hardened steel than titanium bits?
Can I use a standard HSS bit on hardened steel with cutting oil?
What RPM should I use for drilling hardened steel with a cobalt bit?
Do I need a center punch for a 135° split point bit on hardened steel?
How many holes can I expect from a single M35 cobalt bit in hardened steel?
Final Thoughts: The Verdict
For most users, the bits for drilling hardened steel winner is the Norseman 44170 because it delivers aerospace-grade precision and durability that outlasts any other HSS set in this guide. If you want the most comprehensive cobalt set with fractional, letter, and wire sizes all in one box, grab the CaRoller 115-Piece Cobalt Set. And for the budget-conscious DIYer who needs a reliable entry point into cobalt bits, nothing beats the value of the DelitonGude 13-Piece Cobalt Set.