A studio photograph of the Bosch CO21B 21-piece cobalt drill bit set in its original retail packaging, featuring a clear-faced plastic case that shows the assorted bits and 10X life branding.
A studio photograph displaying the full 21-piece assortment of gold-colored cobalt M42 twist drill bits, arranged by size from largest to smallest to show the variety of diameters.
A close-up studio photograph of a single cobalt drill bit with callouts identifying the split point on bits 1/8 inch and larger, the surface-hardened tip, thick web-helix design, and the three-flat shank.
An action photograph showing a Bosch cobalt drill bit penetrating a thick metal plate, creating long metal shavings to demonstrate its high-speed material removal.
An action photograph of a cobalt drill bit being used to drill into a clamped metal workpiece, demonstrating the durability of the bit in a workshop setting.
An instructional graphic displaying five materials the bits are best suited for: cast iron, titanium, aluminum, stainless steel, and light-gauge metal.
An action photograph showing a Bosch drill equipped with a cobalt M42 bit drilling into a metal surface covered in shavings, with the storage case visible in the foreground.
A studio photograph of the Bosch CO21B 21-piece cobalt drill bit set in its original retail packaging, featuring a clear-faced plastic case that shows the assorted bits and 10X life branding.
A studio photograph displaying the full 21-piece assortment of gold-colored cobalt M42 twist drill bits, arranged by size from largest to smallest to show the variety of diameters.
A close-up studio photograph of a single cobalt drill bit with callouts identifying the split point on bits 1/8 inch and larger, the surface-hardened tip, thick web-helix design, and the three-flat shank.
An action photograph showing a Bosch cobalt drill bit penetrating a thick metal plate, creating long metal shavings to demonstrate its high-speed material removal.
An action photograph of a cobalt drill bit being used to drill into a clamped metal workpiece, demonstrating the durability of the bit in a workshop setting.
An instructional graphic displaying five materials the bits are best suited for: cast iron, titanium, aluminum, stainless steel, and light-gauge metal.
An action photograph showing a Bosch drill equipped with a cobalt M42 bit drilling into a metal surface covered in shavings, with the storage case visible in the foreground.
BOSCH

Bosch Cobalt Drill Bit Set CO21B 21 Piece (M42 8 Percent Alloy 135 Deg Split Point Three Flat Shank Metal Hole Boring Tool Case)

In stock
SKU: CO21B
$70.79 USD

Description

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Production-Grade 21-Piece M42 Cobalt Metal Drill Bit Set with Storage Case

The Bosch CO21B 21-Piece Cobalt Metal Drill Bit Set operates as a high-density metalworking hole-boring system engineered to drill stainless steel, cast iron, titanium, and high-temp alloys. Manufactured from M42 high-speed steel alloy containing 8% cobalt, these jobber-length twist bits withstand extreme thermal friction while delivering up to 10X the service life of standard carbon steel cutters. Featuring a thick web-helix geometry for maximum core strength and rapid chip evacuation, all bits 1/8-inch and larger incorporate a 135-degree split point that eliminates bit walking without requiring a center punch, while sizes 3/16-inch and larger utilize a three-flat shank to prevent slippage inside 3/8-inch and 1/2-inch keyless drill chucks.

Best Used For:

  • Stainless Steel & Titanium Sheet Drilling: Boring clean, precise fastener and rivet holes through abrasive 304/316 stainless steel plates and titanium sheets.
  • Cast Iron & Structural Steel Fabrication: Penetrating dense gray cast iron blocks, structural I-beams, and hardened tool steels without cutter dulling.
  • High-Torque No-Slip Hole Production: Executing high-torque drilling passes with bits 3/16-inch and larger using the three-flat shank to eliminate chuck spin.

Key Performance & Safety Features

  • M42 Alloy with 8% Cobalt: Premium cobalt formulation provides extreme heat resistance and 10X operational life in abrasive metals.
  • 135-Degree Self-Centering Split Point: Eliminates bit skate on smooth metal surfaces for instant, punch-free hole starting on sizes 1/8-inch and larger.
  • Three-Flat Shank Design: Surface flats on sizes 3/16-inch and larger ensure positive clamping pressure in keyless drill chucks to prevent spinning.
  • Reinforced Thick Web-Helix Core: Enhanced core cross-section resists rotational snapping forces under heavy vertical feed pressure.
  • Heavy-Duty Jobber Case: Includes a high-impact storage case with labeled size slots to protect cutting tips and simplify bit selection.

What's Included

  • (2) 1/16" M42 Cobalt Drill Bits
  • (2) 5/64" M42 Cobalt Drill Bits
  • (1) 3/32" M42 Cobalt Drill Bit
  • (1) 7/64" M42 Cobalt Drill Bit
  • (2) 1/8" M42 Cobalt Drill Bits
  • (1) 9/64" M42 Cobalt Drill Bit
  • (1) 5/32" M42 Cobalt Drill Bit
  • (1) 11/64" M42 Cobalt Drill Bit
  • (2) 3/16" M42 Cobalt Drill Bits
  • (1) 13/64" M42 Cobalt Drill Bit
  • (1) 7/32" M42 Cobalt Drill Bit
  • (1) 15/64" M42 Cobalt Drill Bit
  • (2) 1/4" M42 Cobalt Drill Bits
  • (1) 5/16" M42 Cobalt Drill Bit
  • (1) 3/8" M42 Cobalt Drill Bit
  • (1) 1/2" M42 Cobalt Drill Bit
  • (1) Heavy-Duty Storage Case

Technical Specifications

Brand Name Bosch Tools
Model Number SKU CO21B
Tool Classification Cobalt Metal Drill Bit Set
Metallurgy Composition M42 High Speed Steel (8% Cobalt Alloy)
Total Set Piece Count 21 Drill Bits + 1 Case
Tip Angle Geometry 135° Split Point (1/8 in. and larger)
Shank Interface Style Three-Flat Shank (3/16 in. and larger) / Round Shank
Bit Length Style Standard Jobber Length Twist Bits
Diameter Range Capacity 0.0625 in. to 0.50 in. (1/16 in. to 1/2 in.)
Product Weight 1.19 lbs.
Target Cutting Substrates Stainless Steel, Cast Iron, Titanium, Hardened Steel, Aluminum
Machine Compatibility Handheld Drill Drivers, Drill Presses, Magnetic Drills

Pro-Tip: When drilling stainless steel or titanium with M42 cobalt bits, run your drill at slow RPM settings with firm, constant feed pressure, and apply cutting fluid or tapping oil directly to the tip. Maintaining slow speeds prevents work-hardening of the metal substrate and preserves the 135-degree split point cutting edges.