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Hardened steel is tough on drill bits. If you have ever tried to bore through an old bolt, a worn die, or a broken tool part, you know how fast an ordinary bit dulls or overheats. Parts like these often sit in the 42 to 65 Rockwell C range, so the right bit matters. Check the bit material, whether the maker says it is made for hardened metal, the point angle, and the shank, since a slipping shank wastes torque on hard work.
Our top pick is the Crosstar M35 cobalt set. It makes the most direct hardened-metal claim of the group, and it has a titanium aluminum nitride coating and a three-flat shank for a secure grip. Here is what's available right now, from a single bit to larger sets.
1 Crosstar M35 Cobalt Drill Bit Set, 21 Pieces, TiAlN Coated | 2 Diablo Metal Demon Drill Bit Set, 29 Piece, 130 Degree Hybrid Split Point | 3 MACXCOIP 13-Piece Cobalt Drill Bit Set, 1/16 to 1/4 Inch | 4 Bosch CO14B 14-Piece Cobalt Drill Bit Set with Case | 5 COMOWARE M35 Cobalt Drill Bit Set, 99 Pieces, Tri-Flat Shanks | 6 Sinyeenglon Cobalt Drill Bit Set, 122 Pieces, 1/16 to 1/2 Inch | |
|---|---|---|---|---|---|---|
| Best for | Best overall | Best one-bit option | Best budget | Best known brand | Most sizes, two-flute | Largest set |
| Material | M35 cobalt high-speed steel (5% cobalt) | Not listed | M35 cobalt | M42 cobalt (8% cobalt, per listing) | M35 cobalt | M35 cobalt |
| Size range | 1/16 to 1/2 inch | Not listed | 1/16 to 1/4 inch | 1/16 to 1/2 inch | Not listed | 1/16 to 1/2 inch |
| Pieces | 21, with index storage case | 29 | 13, with index storage case | 14, with case | 99 in 1/16 to 3/8 inch sizes | 122, with index storage case |
| Shank | Three-flat | 3-flats | Not listed | Not listed | Round and tri-flat | Not listed |
| Stated hardness | Up to 60 HRC (manufacturer figure) | Mild, hardened and stainless steel (manufacturer) | Not listed | Not listed | Not listed | Up to 67 (manufacturer figure) |
| Point | Not listed | 130 degree hybrid split point | 135 degree | Not listed | 135 degree split point | Not listed |
| Check price at Amazon | Check price at Amazon | Check price at Amazon | Check price at Amazon | Check price at Amazon | Check price at Amazon |
Crosstar M35 Cobalt Drill Bit Set, 21 Pieces, TiAlN CoatedBest overallMost recommended by reviewers
Check price at Amazon
Diablo Metal Demon Drill Bit Set, 29 Piece, 130 Degree Hybrid Split PointBest one-bit option
MACXCOIP 13-Piece Cobalt Drill Bit Set, 1/16 to 1/4 InchBest budget
Bosch CO14B 14-Piece Cobalt Drill Bit Set with CaseBest known brand
COMOWARE M35 Cobalt Drill Bit Set, 99 Pieces, Tri-Flat ShanksMost sizes, two-flute
Sinyeenglon Cobalt Drill Bit Set, 122 Pieces, 1/16 to 1/2 InchLargest set
A 21-piece three-flute cobalt set with the most direct hardened-metal claim on this page.
Most recommended by reviewers
Check price at AmazonPrices and availability on Amazon change often.
One catchThe smallest sizes, 1/16 to 7/64 inch, use a two-flute design, so the three-flute benefits only apply to the larger bits.
This set has the most specific hardened-metal claim on the shortlist. The listing names hardened metal as a target, rates the drilling hardness up to 60 HRC, and pairs M35 cobalt with a TiAlN coating for heat resistance. Forum advice on hard steel stresses heat, so a heat-rated coating and cobalt base point in the right direction.
The three-flat shank is the practical bonus. It keeps the bit from spinning in the chuck under high torque, which matters when a bit is loaded and stalled on hard steel. The 21 sizes cover most common fractional holes in one case.
A coated 29-piece set that the maker says covers mild, hardened and stainless steel with one bit type.
Prices and availability on Amazon change often.
If you work across mild steel, stainless and hardened parts, one set that covers all three saves buying several bit types. The listing describes a thermal coating that is meant to keep the cutting edge cooler, and a 130 degree split point for accurate starts without walking.
Its claims are bold, including 30 times longer life and drilling up to twice as fast. Treat those as the maker's figures. The set costs the most on this shortlist, so it suits people who drill many different metals and want to avoid buying separate sets.
The lowest-cost cobalt set on this page, covering the common small sizes.
Prices and availability on Amazon change often.
For a small job, a 13-piece cobalt set covers most of the small holes you will need on hardened parts. The listing describes a 135 degree point and self-centering design, and a case that makes sizes easy to find.
It is the cheapest option here, so it is a good first set for trying cobalt on hard metal. If you need holes above 1/4 inch, buy a larger set instead.
A name-brand jobber set with a case, sized for everyday metal work.
Prices and availability on Amazon change often.
If you prefer a known brand, this Bosch set is the most recognizable name here. It uses M42 cobalt with a surface-hardened tip, and the listing names hardened steel and stainless as target materials.
The thick web design is listed as adding stability, which helps when the bit meets hard steel. With 14 sizes, it covers the common holes without the bulk of the larger sets.
A 99-piece set with round and tri-flat shanks and a partitioned case.
Prices and availability on Amazon change often.
If you want many sizes in one case, this 99-piece set goes further than most. The listing describes an M35 cobalt base, a 135 degree split point, and a partitioned case that keeps sizes from mixing.
The set uses two flutes, which the maker says clear chips quickly and keep the bit cooler. It stops at 3/8 inch, so pair it with a larger bit if you need a 1/2 inch hole.
The most pieces on this page, weighted toward the small sizes you use most.
Prices and availability on Amazon change often.
For a shop that drills many small holes, this set puts the most bits where they are used. The listing shows extra pieces in the 1/16 and 5/64 inch sizes, with fewer in the larger ones.
The plastic case is labeled by size on the lid, so bits are easy to find. The hardness figure of 67 is the maker's, so check it against your own material needs.
Hobbyists and home mechanics who drill hardened bolts occasionally will do well with the Crosstar or the 13-piece budget set. Machinists and fabricators who work across mild steel, stainless and hardened parts may prefer the Diablo one-bit option, or a larger set for more sizes.
If you need a specific hole size often, the larger sets from Sinyeenglon and COMOWARE save time on size changes.
Retail and reader advice both say standard high-speed steel and cobalt bits can stop on fully hardened steel. For that job, carbide is the material most often recommended, and reader discussions say it needs a rigid setup and a fixture.
Gold-colored titanium-coated bits are a poor choice for this work. One forum commenter called them low-grade junk, and cobalt is preferred because it can be resharpened.
If a hole is critical or the steel is very hard, a machine shop with a lathe or mill is the safer choice, and some suggest EDM for hardened parts.
For fully hardened steel, carbide is the material most often recommended by reader discussions and retailer guides. Among the cobalt sets on this page, the Crosstar M35 set has the most direct hardened-metal claim, with a TiAlN coating and a three-flat shank.
Carbide is harder than cobalt high-speed steel, which is why it is usually the choice once steel is fully hardened. Carbide is also brittle and needs a rigid setup, while cobalt is tougher and can be resharpened.
Use a rigid setup and a fixture, drill at low speed with steady pressure, and use cutting oil on the cutting face. Start with a small pilot hole and a short bit, and drill in short stops so the edge does not overheat.
Gold-colored titanium-coated bits are generally a poor choice for hardened steel. A reader called them low-grade, and cobalt bits are preferred for tough metal because they can be resharpened.
No single brand stands out in the research for this job. Most sets here are M35 cobalt from different makers, and Bosch is the best-known name with a case. Choose by size range, point angle and shank type.
Local hardware stores often carry inexpensive masonry bits, which one machinist suggests grinding with extra clearance for hard metal. A machine shop can also drill hardened parts for you, and the sets on this page are sold on Amazon.
Why trust BullseyeBuy
Every set on this page was checked on Amazon for the exact configuration shown and is in stock. Picks are ranked on what each listing says about hardened metal, material, set size and shank design, weighed against the advice of machinists and reader forums on drilling hard steel.
Our expert team tests products when it is needed and researches online and in interviews. Every guide is fact-checked and edited by a real person.
The BullseyeBuy editorial team · Updated Oct 17, 2026
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