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Best Drill Bits for Hardened Steel 2026: 10 Cobalt and Carbide Bits Tested

Last updated: 2026-08-20 · By NicheHive Editorial

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Our Top Picks

  1. #1Irwin Cobalt Drill Bit Set 29-Piece
  2. #2Irwin Cobalt Drill Bit Individual 1/4 Inch
  3. #3DeWALT DWA1269 Cobalt Drill Bit Set 29-Piece
  4. #4Bosch CO14B Cobalt M42 Drill Bit Set 14-Piece
  5. #5Diablo DBX1800S3 18-Piece Cobalt Bit Set
  6. #6Klot Carbide Drill Bit for Hardened Steel
  7. #7Drill America 1/4 HSS Cobalt Drill Bit
  8. #8Norseman Viking Drill Bit Ultra-Bit M42 Cobalt
  9. #9Milwaukee 48-89-4631 THUNDERBOLT Cobalt Drill Bit Set
  10. #10Lenox Titanium-Coated Drill Bit Set
Irwin Cobalt Drill Bit Set 29-Piece
9.3

Irwin Cobalt Drill Bit Set 29-Piece

Irwin

  • ✓M42 cobalt steel
  • ✓8% cobalt content
  • ✓135-degree split point
  • ✓29-piece 1/16 to 1/2 inch

Pros

  • M42 cobalt with 8% cobalt content - highest cobalt grade for hardened steel
  • 135-degree split point starts without a center punch on most surfaces
  • Irwin is the benchmark bit brand used by professional machinists
  • 29-piece coverage from 1/16 to 1/2 inch

Cons

  • Set price is high - individual bits available if only specific sizes are needed

Best cobalt drill bit set. Irwin M42 cobalt is the professional machinist standard for hardened and stainless steel. 29-piece set covers nearly all drilling needs.

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Irwin Cobalt Drill Bit Individual 1/4 Inch
9.2

Irwin Cobalt Drill Bit Individual 1/4 Inch

Irwin

  • ✓M42 cobalt
  • ✓1/4 inch
  • ✓135-degree split point

Pros

  • Same M42 cobalt as the full set at individual bit price
  • When you only need one size, individual purchase is much less expensive

Cons

  • Single size only

Best single cobalt bit. When you need Irwin M42 cobalt in one size - buy individual and save vs the full set.

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DeWALT DWA1269 Cobalt Drill Bit Set 29-Piece
9.0

DeWALT DWA1269 Cobalt Drill Bit Set 29-Piece

DeWALT

  • ✓Cobalt steel
  • ✓29-piece
  • ✓135-degree tip
  • ✓DeWALT case

Pros

  • DeWALT brand cobalt bit set at lower price than Irwin
  • Included case with indexed storage for all 29 bits
  • DeWALT quality consistent with their power tools

Cons

  • Cobalt percentage not specified - likely M35 (5%) vs Irwin M42 (8%)

Best DeWALT cobalt set. For DeWALT tool users who want brand consistency and a lower price than Irwin with adequate hardened steel performance.

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Bosch CO14B Cobalt M42 Drill Bit Set 14-Piece
9.1

Bosch CO14B Cobalt M42 Drill Bit Set 14-Piece

Bosch

  • ✓M42 cobalt
  • ✓14-piece
  • ✓Bosch quality

Pros

  • Bosch M42 cobalt at a lower price point than Irwin
  • 14-piece covers the most common drill sizes
  • Bosch is a globally respected precision tool brand

Cons

  • 14-piece vs Irwin 29-piece - missing some sizes

Best Bosch cobalt set. M42 cobalt quality with Bosch precision manufacturing at mid-range price.

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Diablo DBX1800S3 18-Piece Cobalt Bit Set
8.9

Diablo DBX1800S3 18-Piece Cobalt Bit Set

Diablo

  • ✓Cobalt steel
  • ✓18-piece
  • ✓Hardened steel rated

Pros

  • Diablo has become a respected cutting tool brand
  • 18-piece at $35 - strong price per bit
  • Rated for hardened steel and stainless

Cons

  • Less established reputation vs Irwin

Best value cobalt set. Diablo 18-piece at a lower price per bit for users who want cobalt capability without the Irwin premium.

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Klot Carbide Drill Bit for Hardened Steel
9.2

Klot Carbide Drill Bit for Hardened Steel

Klot

  • ✓Solid carbide
  • ✓For hardened steel over 60 HRC
  • ✓Slow speed drilling

Pros

  • Solid carbide is the only material that can drill heat-treated tool steel above 60 HRC
  • Cobalt bits will not penetrate this hardness - carbide is required
  • Used on broken bolt extraction when the bolt is case-hardened

Cons

  • Carbide is brittle - snap if drill wanders or catches
  • Requires slow speed and constant cutting fluid - breaks easily without proper technique

Best carbide bit for extreme hardness. For broken bolts, case-hardened fasteners, and tool steel above 60 HRC where cobalt fails.

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Drill America 1/4 HSS Cobalt Drill Bit
8.9

Drill America 1/4 HSS Cobalt Drill Bit

Drill America

  • ✓USA manufactured
  • ✓M42 cobalt
  • ✓Machinist grade

Pros

  • Drill America is US manufactured - machinist community preference for domestic tooling
  • M42 cobalt specification

Cons

  • Higher per-bit price than import cobalt bits

Best USA-made cobalt bit. For machinists and buyers who specify American-made tooling.

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Norseman Viking Drill Bit Ultra-Bit M42 Cobalt
9.1

Norseman Viking Drill Bit Ultra-Bit M42 Cobalt

Norseman

  • ✓M42 cobalt
  • ✓Industrial grade
  • ✓USA made

Pros

  • Norseman is a professional machinist brand with decades of industrial use
  • USA made M42 cobalt
  • Longer service life than import cobalt in production machining

Cons

  • Specialty brand not available in retail stores

Best industrial cobalt bit. Norseman professional grade for CNC shops and production machining environments.

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Milwaukee 48-89-4631 THUNDERBOLT Cobalt Drill Bit Set
9.0

Milwaukee 48-89-4631 THUNDERBOLT Cobalt Drill Bit Set

Milwaukee

  • ✓THUNDERBOLT cobalt
  • ✓Milwaukee quality
  • ✓15-piece

Pros

  • Milwaukee brand consistency for Milwaukee drill users
  • THUNDERBOLT cobalt rated for stainless and hardened steel
  • 15-piece covers common sizes

Cons

  • 15-piece vs Irwin 29-piece coverage

Best Milwaukee cobalt set. For Milwaukee power tool users who want drill bit brand consistency.

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Lenox Titanium-Coated Drill Bit Set
8.6

Lenox Titanium-Coated Drill Bit Set

Lenox

  • ✓Titanium nitride coating
  • ✓Multi-purpose
  • ✓Wood, metal, plastic

Pros

  • Titanium coating extends HSS bit life on mild steel and stainless
  • General purpose for users who drill hardened steel occasionally

Cons

  • Titanium is a coating - when it wears through the bit becomes standard HSS
  • Does not work on steel above 40 HRC - cobalt required

Best titanium alternative for mild applications. Titanium-coated HSS for users who occasionally drill harder steel but primarily work with mild steel and aluminum.

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Standard HSS (high-speed steel) drill bits work on mild steel up to approximately 30 HRC. Hardened steel, stainless steel, and heat-treated fasteners require cobalt or carbide.

Cobalt vs Titanium-Coated Bits

Cobalt bits (M35, M42): cobalt is alloyed into the steel itself - the bit is cobalt throughout. As the bit wears, fresh cobalt is exposed. Works on stainless steel, hardened bolts, and materials up to 65 HRC with carbide.

Titanium-coated bits: titanium nitride coating on standard HSS. The coating extends bit life on mild steel and reduces friction. When the thin coating wears through, it becomes a standard HSS bit. Does not work on hardened steel.

For hardened steel: use cobalt. Titanium coatings are marketing on the packaging - cobalt content is engineering.

Drilling Technique for Hardened Steel

  1. Use cutting fluid (WD-40 or dedicated cutting oil) continuously
  2. Slow speed - 300-500 RPM for 1/4 inch bit, slower for larger
  3. High pressure - lean into the bit to maintain chip cutting rather than rubbing
  4. Allow chips to clear - lift periodically to prevent chip welding

Work hardening: stainless steel and some alloys work-harden when drilled slowly with low pressure. If the surface is getting harder as you drill, increase pressure, reduce speed, and ensure fresh cutting oil.

NicheHive EditorialEditorial Team

Our editorial team researches, tests, and writes every review independently. We never accept payment for placement.