Cobalt drill bits are often recommended for stainless steel, but buyers still need to choose the right grade. The two common names are M35 and M42.
The short answer: M35 is usually the practical choice for most stainless steel drilling. M42 is the premium option for tougher, hotter and more production-focused applications.
M35 vs M42 Quick Comparison
| Grade | Typical cobalt content | Best use | Trade-off |
|---|---|---|---|
| M35 | About 5% cobalt | 304/316 stainless steel, harder steel, general workshop drilling | Better value, less brittle than M42 |
| M42 | About 8% cobalt | Production stainless drilling, heat-heavy jobs, tougher alloys | Higher cost and more brittleness |
Why Cobalt Helps
Cobalt improves hot hardness. That means the cutting edge keeps hardness better when drilling stainless steel and tougher metals. This matters because stainless steel holds heat near the cutting zone and can work-harden if the drill rubs.
When to Choose M35
M35 is the better starting point for most importers because it balances performance and cost. It is suitable for common stainless steel drilling, repair work, fabrication shops and mixed metal users.
When to Choose M42
M42 makes sense when the customer drills stainless steel in production volume, when tool changes are costly, or when M35 does not last long enough. But it should be used with proper speed, feed and workholding.
Buyer Takeaway
For most distributors, offer M35 as the standard cobalt line and M42 as a premium industrial line. Link cobalt recommendations to real applications, not just “more cobalt is better.” For related selection logic, see Drill Bit for Stainless Steel, Drill Bit Materials Explained, and Drill Speed Chart.