Understanding HSS Grades: M2, M35, and M42
When sourcing HSS drill bits for industrial use, the steel grade is the single most important specification. It determines how long your bits last, what materials they can cut, and ultimately your cost per hole. Yet many buyers default to M2 simply because it is the most common — often leaving performance and money on the table.
At JacoTools, we smelt our own high-speed steel in M1, M2, M35, and M42 grades, so we understand these materials from the molecular level up. Here is a practical breakdown.
M2 HSS — The Industry Workhorse
M2 (also called 6-5-2 for its tungsten-molybdenum-vanadium content) is the most widely used HSS grade worldwide. It offers a strong balance of hardness (typically 63–65 HRC after heat treatment), toughness, and grindability.
Best for: General-purpose drilling in mild steel, aluminum, cast iron, wood, and plastics. If your shop runs mixed materials and moderate volumes, M2 is the cost-effective default.
Limitations: M2 starts losing hardness above 600°C. When drilling stainless steel, hardened alloys, or running at high RPM without coolant, M2 bits dull quickly.
M35 HSS — The Cobalt Advantage
M35 adds 5% cobalt to the M2 base composition. This raises the red hardness — the temperature at which the steel retains its cutting edge — from roughly 600°C to 650°C. Hardness increases to 65–67 HRC.
Best for: Stainless steel (304, 316), heat-treated steels, titanium alloys, and any application where the cutting edge gets hot. M35 is the go-to upgrade when M2 bits are burning out too fast.
Cost consideration: M35 typically costs 15–25% more than M2. But if you are replacing M2 bits every 50 holes in stainless and M35 lasts 150+ holes, the per-hole cost drops significantly.
M42 HSS — Maximum Heat Resistance
M42 contains 8% cobalt and reaches 67–69 HRC. It maintains cutting ability at temperatures up to 700°C, making it the hardest conventional HSS grade available.
Best for: Aerospace alloys (Inconel, Hastelloy), hardened tool steels above 35 HRC, and high-production environments where downtime for bit changes is expensive. M42 is also the standard tooth material for professional bi-metal hole saws.
Trade-off: Higher hardness means slightly more brittleness. M42 bits are less forgiving of side loads and deflection. They perform best in rigid setups — drill presses, CNC machines — rather than handheld drills.
Quick Comparison Table
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How to Choose: A Practical Decision Framework
1. What material are you drilling? If it is mild steel, aluminum, or wood — M2 is sufficient. If stainless or alloy steel — go M35. If aerospace superalloys or hardened steel — M42.
2. What is your production volume? Higher volumes generate more heat. Even in mild steel, a high-speed CNC operation may benefit from M35 for longer tool life.
3. What is your setup rigidity? Handheld drilling favors the toughness of M2 or M35. Rigid machine setups can take full advantage of M42 hardness.
4. Calculate cost per hole, not cost per bit. A $3 M42 bit that drills 200 holes costs $0.015/hole. A $1.50 M2 bit that drills 40 holes costs $0.038/hole.
Why Material Source Matters
The grade designation only tells part of the story. The quality of the raw steel — its purity, carbide distribution, and heat treatment — varies enormously between manufacturers. This is why JacoTools operates its own steel smelting facility producing 4,800 tons of HSS annually. We control the composition from melt to finished tool, ensuring every M2 bit actually performs like M2 and every M35 bit delivers the cobalt advantage you are paying for.
Need help specifying the right grade for your application? Contact our engineering team at info@jacotools.com.
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