For DIN 338 HSS drill bits, DIN 338 only defines the dimensions and geometry (jobber-length twist drill). It does not specify the steel grade. The difference between M2, M35, and M42 is the type of high-speed steel used to make the drill, which affects hardness, heat resistance, wear life, and cost.

Here's a comparison:

M2 HSS

Best for:

• Mild steel
• Aluminium
• Brass
• Plastics
• General workshop use

Advantages

• Most economical
• Tough and less likely to chip
• Easy to sharpen

Limitations

• Loses hardness sooner when drilling harder materials or at higher temperatures.

M35 (5% Cobalt)

Despite the name, M35 is still HSS—it simply contains about 5% cobalt.

Best for:

• Stainless steel (304, 316)
• Tool steel
• Cast iron
• Harder alloy steels

Advantages

• Better red hardness (keeps its hardness when hot)
• Longer tool life
• More resistant to wear

For many engineering workshops, M35 offers the best balance of price and performance.

M42 (8% Cobalt)

M42 contains approximately 8% cobalt and a higher vanadium content than M35.

Best for:

• Hardened steels
• High-tensile alloys
• Aerospace materials
• Continuous production work
• Tough stainless steels

Advantages

• Highest heat resistance
• Longest tool life
• Maintains cutting edge under heavy loads

Disadvantages

• Most expensive
• Slightly more brittle than M2, so it benefits from rigid setups and correct feeds.

Which should you buy?

Choose M2 if:

• You mostly drill mild steel and aluminium.
• Cost is the priority.
• It's for occasional or DIY use.

Choose M35 if:

• You regularly drill stainless steel.
• You want significantly longer life without a huge price increase.
• It's for professional maintenance or fabrication work.

For most professionals, M35 is the "sweet spot."

Choose M42 if:

• You drill hard alloys every day.
• Downtime from changing drills is costly.
• You're doing production or industrial work where maximum tool life justifies the higher price.

Typical applications

Bottom line

• M2: Best value for general-purpose drilling.
• M35: The best all-round choice for mixed materials, especially if you encounter stainless steel.
• M42: Premium option for demanding industrial applications and difficult-to-machine alloys where extended tool life is the priority.