Bosch CO21B 21-Piece Cobalt M42 Drill Bit Set with Case and Three-Flat Shank

Durable cobalt bits built for tough metals

The Bosch CO21B 21-piece cobalt M42 drill bit set combines rugged construction with practical design. Crafted from an upgraded M42 cobalt alloy containing 8% cobalt, these bits are designed to resist wear and heat, offering up to 10x longer life than standard cobalt bits in typical use. The jobber-length bits balance reach and control, helping you drill through stainless steel, cast iron, titanium, light-gauge metal, and aluminum with steadiness and reduced chatter.

The thick web-helix geometry promotes efficient material removal and steadier cuts, while a surface-hardened tip helps the bit bite into tough surfaces. Bits sized 1/8 in and larger feature a split point to start accurately with less skating, and those 3/16 in and larger include a three-flat shank for improved chuck grip, reducing the chance of slippage during aggressive drilling.

Smart features and practical design

In addition to performance, this kit emphasizes organization and ease of use. The 21 cobalt M42 bits arrive in a sturdy plastic case that keeps bits organized by size and readily portable for job sites or bench sessions. The case design helps minimize downtime and keeps your tools ready for the next project.

• Upgraded M42 cobalt alloy with 8% cobalt for wear resistance and heat tolerance
• Up to 10x longer life versus standard cobalt bits in typical tasks
• High-heat resistance for extended drilling sessions
• Thick web-helix for stable cutting and fast chip removal
• Surface-hardened tip to penetrate hard materials
• Split points on 1/8 in and larger for easy starts
• Three-flat shank on 3/16 in and larger for better chuck grip

What you can tackle with this set

This kit is well suited for stainless steel, cast iron, titanium, light-gauge metal, and aluminum. While outcomes vary with material, drill size, and technique, the set provides a practical option for shop projects, metalworking tasks, and home repairs that require durable, repeatable holes.

• Stainless steel drilling and hard metal work
• Casting and structural metal applications
• Titanium and other hard alloys
• Light-gauge metal and aluminum tasks
• General metalworking and repair projects

Includes a plastic case for organized storage and easy transport, making it a versatile addition to a professional or DIY workspace. For best results, pair with appropriate lubrication and controlled drill speeds. Results may vary by material and technique.