A standard high-speed steel bit dulls instantly against a hardened steel bracket, stainless steel countertop, or cast-iron fitting. That lost time and ruined work piece is the specific frustration that drives serious buyers toward a specialized drill bit for hard metal — one engineered with the correct alloy, tip geometry, and thermal tolerance to chew through tough alloys without chipping or overheating.
I’m Mo Maruf — the founder and writer behind The Tools Trunk. I’ve spent years analyzing drill bit metallurgy, split-point designs, and real-user failure reports to separate the sets that actually cut from the ones that walk and snap under load.
This guide breaks down five M35 cobalt sets that handle the heat and abrasion of machining hard metals, so you can identify the best drill bit for hard metal without wasting money on bits that dull on the first hole.
How To Choose The Best Drill Bit For Hard Metal
Hard metal demands a bit that resists heat softening and maintains a sharp cutting edge under pressure. Three factors separate the durable sets from the disposable ones: the alloy composition, the tip geometry, and the shank design that prevents slippage in the chuck.
M35 Cobalt vs Standard HSS
M35 high-speed steel contains 5% cobalt, which raises the material’s red hardness — the temperature at which the cutting edge begins to soften. Standard HSS loses hardness around 500°C, while M35 holds its edge up to approximately 600°C. For drilling stainless steel, hardened alloys, or cast iron, that extra 100°C of heat tolerance translates directly into fewer trips to the sharpener and less risk of snapping the bit mid-hole.
135° Split Point Is Not Optional
A 135° split point serves two critical roles on hard metal: it self-centers so the bit doesn’t skate across the surface, and it reduces the thrust force required to initiate the cut. Standard 118° points tend to walk on smooth hardened steel and require a center punch to stay on target. The split-point geometry also breaks chips into smaller segments, preventing long stringers that clog flutes and overheat the bit.
Shank Design and Chuck Grip
Round shanks can spin inside a three-jaw chuck under heavy torque, marring both the bit and the tool. The best sets incorporate a three-flat shank on larger diameters — starting around 3/16-inch — so the chuck grips positively and won’t slip even when drilling deep into tough stock.
Size Increment Coverage
A useful set provides continuous increments of 1/64-inch from 1/16-inch up to at least 3/8-inch, and ideally to 1/2-inch. Jumping from 3/16-inch directly to 1/4-inch leaves the user without the intermediate sizes needed for pre-drilling or for fitting standard hardware without excessive reaming.
Quick Comparison
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| Model | Category | Best For | Key Spec | Amazon |
|---|---|---|---|---|
| CaRoller 29pc M35 | Mid-Range | Belt-pack portability & stainless plate | 3-flute design, amber coating | Amazon |
| Yougfin 29pc M35 | Mid-Range | Largest size range in one index | 29 bits, 1/16 to 1/2 inch | Amazon |
| MACXCOIP 25pc Metric M35 | Premium | Metric machining & CNC work | 1.0 mm to 13.0 mm coverage | Amazon |
| WildBossy 20pc M35 | Budget | Budget-friendly general hard metal use | 5% cobalt, 67 HRC rating | Amazon |
| STROTON 21pc M35 | Budget | Value-driven stainless & bolt drilling | Q235 steel case, 68 HRC | Amazon |
In‑Depth Reviews
1. CaRoller 29-Piece M35 Cobalt Drill Bit Set
The CaRoller set stands out for its belt-clip cup-style case — a practical detail for tradespeople who need bits at arm’s reach without carrying a full index case. The amber coating adds a thin protective layer that resists corrosion, though the real cutting performance comes from the M35 substrate underneath. Users report clean spiral chips from 1/8-inch stainless plate when running a drill press at 300 RPM with cutting oil, indicating proper edge geometry and heat dissipation.
The kit includes 29 bits spanning 1/16-inch to 1/2-inch, and the 135-degree split point self-centers reliably on smooth surfaces. A three-flute design on certain sizes helps clear chips faster in deep holes, though the round shanks on smaller diameters may require careful chuck tightening to avoid slippage under heavy feed pressure.
One durability concern emerged from users: the cup-style holder fits tightly, and some bits show shank marring when forced back into the slots. This is a handling issue rather than a bit quality issue, but it means the case may not last through years of daily use. For the mid-range price tier, however, the combination of M35 material, broad size range, and job-site portability makes this a compelling pick.
What works
- Belt-clip cup case keeps bits accessible during repetitive drilling
- Amber coating reduces surface rust in humid environments
- 135° split point prevents walking on slick stainless surfaces
What doesn’t
- Cup holder slots are tight and may mar shanks on reinsertion
- Round shanks lack anti-spin flats on smaller sizes
2. Yougfin 29-Piece M35 Cobalt Drill Bit Set
The Yougfin 29-piece set offers the widest fractional size coverage in this roundup, jumping in 1/64-inch increments from 1/16-inch all the way to 1/2-inch. This level of granularity matters when you need to drill a precise pilot hole before stepping up to a larger diameter — common in bolt extraction and hardened steel work where oversized holes weaken the joint. The M35 alloy delivers the 5% cobalt content needed to cut alloy steel and stainless without edge breakdown.
Users consistently note the bits arrive sharp enough to drill through 5/8-inch steel with minimal wear over repeated holes. The 135° split-point geometry reduces walk-off on curved or uneven surfaces, and the bright finish helps users visually inspect for micro-chipping after use. The plastic index case holds every bit securely, though a few reports mention hinge fragility after repeated opening cycles.
The biggest limitation is the index case itself — several users experienced early hinge failure, which turns an organized 29-bit set into a loose collection. The bits themselves perform well enough that many simply transfer them to a separate storage solution. For home workshop use where the case stays on a shelf, this is a minor annoyance; for mobile use, it may frustrate. Still, the combination of M35 material and continuous size coverage justifies the mid-range price.
What works
- 29 sizes in 1/64-inch steps cover nearly every fractional need
- Split-point tip self-centers reliably on flat steel surfaces
- Bits hold edge well through dozens of holes in mild steel
What doesn’t
- Plastic index case hinges are prone to early breakage
- No three-flat shanks on intermediate sizes increase spin risk in chuck
3. MACXCOIP Metric 25-Piece M35 Cobalt Drill Bit Set
The MACXCOIP set is the only metric offering among these five, covering 1.0 mm up to 13.0 mm in 0.5 mm steps. This specificity is invaluable for CNC machinists, 3D-print post-processors, and anyone working with European hardware where fractional-inch bits require inconvenient conversion and reaming. The M35 alloy provides the same thermal resilience as the other cobalt sets, but the metric sizing eliminates the guesswork when drilling for M3 through M12 fasteners.
Former machinists who reviewed this set confirm the bits cut accurately and hold up under production conditions. The 135° split-point reduces walking, and the straight shanks grip well in collet-style chucks common on milling machines. Users drilling hardened steel report clean, free-cutting action as long as spindle speed stays moderate and cutting fluid is applied — the bits show no micro-chipping after repetitive use in alloy steel.
The flat plastic index case fits neatly into shallow toolbox drawers, a thoughtful design for organized shops. However, one user noted that a bit slipped in a drill-press chuck, deforming the shank slightly — suggesting the hardness may be concentrated at the cutting tip rather than throughout the full shank length. For most metric drilling applications, this is a minor trade-off given the premium price tier and the unique sizing advantage.
What works
- Metric sizing in 0.5 mm increments matches European hardware precisely
- M35 alloy handles repetitive production drilling in alloy steel
- Flat case stores easily in shallow tool chest drawers
What doesn’t
- Shank hardness may be lower than the cutting tip, risking deformation under high torque
- No fractional-inch sizes — not a hybrid set
4. WildBossy 20-Piece M35 Cobalt Drill Bit Set
The WildBossy set delivers a budget-friendly entry into M35 cobalt bits without cutting corners on the critical spec — the 5% cobalt alloy. The manufacturer claims a Rockwell hardness of 67 HRC, which aligns with the expected hardness range for M35 material. Bits in this set have been used successfully to drill out broken taps and studs in turbo housings, a real-world test that separates genuine cobalt from surface-coated imitations.
The 135° split-point and three-flat shanks on larger diameters help prevent walking and chuck slippage — features typically reserved for more expensive kits. The titanium surface finish adds a layer of lubricity that reduces friction in softer materials, though its real benefit on hard metal is marginal once the coating wears at the cutting edge. Users drilling thin stainless steel report the bits cut through cleanly with slow RPM and lubrication.
The main drawback is manufacturing consistency. Multiple users reported that some bits in the set arrived either dull or snapped during initial use, suggesting variable quality control in the sharpening process. For the budget-conscious buyer who needs cobalt capability for occasional hard-metal drilling, the set offers strong value; for daily production use, the inconsistency would be frustrating. The plastic storage case is basic but functional for keeping sizes organized.
What works
- Genuine M35 cobalt at a budget-friendly price point
- Three-flat shanks on larger diameters prevent chuck slippage
- Proven capable of drilling out hardened studs and taps
What doesn’t
- QC issues: some bits arrive dull or snap on first use
- Only 20 pieces — fewer intermediate sizes than premium sets
5. STROTON 21-Piece 5% Cobalt Drill Bit Set
The STROTON 21-piece set covers the most commonly used fractional sizes from 1/16-inch to 3/8-inch in tight 1/64-inch increments, omitting the half-inch bit that other sets include. This makes it a focused kit for users whose largest drilled hole rarely exceeds 3/8-inch — common in automotive, HVAC, and general fabrication work. The M35 alloy with a stated 68 HRC rating gives it a slight edge in hardness over the WildBossy set, and user reports confirm the bits stay sharp through extended use.
The steel index case is the standout differentiator here: made from Q235 cold-rolled steel, it resists crushing and hinge failure far longer than plastic alternatives. The 135° split-point and three-flat shanks on bits 3/16-inch and larger deliver the anti-spin reliability needed for drill-press work.
The only significant issue is that the rivets attaching the index to the case can loosen over time, requiring the user to drill out and replace them with small nuts and bolts. This is a one-time fix for an otherwise robust case. The round shanks on sizes below 3/16-inch lack flats, so those smaller bits may spin in a chuck under heavy load. For the budget price tier, the STROTON set offers excellent hole-per-dollar value.
What works
- Steel case outlasts plastic indices by a wide margin
- 3-flat shanks on bits 3/16-inch and larger prevent chuck slip
- Bits hold sharpness through hundreds of holes in steel
What doesn’t
- Rivets holding the index to the case may fail and need replacement
- No half-inch bit — maximum diameter is 3/8-inch
Hardware & Specs Guide
M35 Cobalt Alloy
M35 high-speed steel contains approximately 5% cobalt by weight, along with molybdenum and vanadium. The cobalt addition raises the material’s red hardness — the temperature at which the cutting edge begins to plastically deform — from roughly 500°C for standard M2 HSS to about 600°C for M35. This 100°C headroom means the bit maintains its edge geometry longer when drilling hard metals that generate frictional heat at the cutting interface.
135° Split Point
A split point is created by grinding a secondary facet across the chisel edge of a drill bit. The 135° angle is blunter than the standard 118° point, meaning more of the cutting edge contacts the work surface simultaneously upon entry. This reduces the axial force needed to start the hole and eliminates the need for center punching on most surfaces. The split itself creates a self-centering effect that prevents the bit from walking sideways.
Three-Flat Shank
A three-flat shank has three machined flats ground into the cylindrical shank surface. When clamped in a three-jaw chuck, these flats provide positive mechanical interlock that prevents the bit from spinning under high torque loads. Typically found on bits 3/16-inch and larger, this feature is critical when drilling hard metal at low RPM with high feed pressure.
Amber Coating vs TiN
Amber coating is a thin decorative or anti-corrosion layer, typically a variant of titanium nitride or a proprietary amber-colored surface treatment. It provides marginal lubricity and rust resistance but wears off quickly at the cutting edge during hard-metal use. Titanium nitride (TiN) is a harder, gold-colored ceramic coating that reduces friction and improves chip flow, but its benefit on cobalt bits is secondary to the alloy itself.
FAQ
Can I use a cobalt drill bit without cutting oil?
What RPM should I run for drilling hardened steel?
How do I know if a drill bit is genuine M35 cobalt?
Can I sharpen a dull cobalt drill bit at home?
Final Thoughts: The Verdict
For most users, the drill bit for hard metal winner is the Yougfin 29-Piece M35 Cobalt Set because its continuous 1/64-inch size steps from 1/16-inch to 1/2-inch cover nearly every fractional requirement without gaps. If you need a portable kit that clips to your belt for job-site drilling, the CaRoller 29-Piece Set with its cup-style case is the practical choice. And for metric machining work that demands precise sizing for European hardware, nothing beats the MACXCOIP Metric 25-Piece Set.