What Are Cobalt Drill Bits? | Hard-Metal Specialists Explained

If you’ve ever watched a standard bit smoke and dull against a stainless steel plate, you already know why cobalt drill bits exist. The cobalt is mixed into the steel itself, not painted on as a coating, which is what lets these bits run hot and keep cutting through abrasive metals that ruin ordinary HSS bits.

What Makes Cobalt Bits Different From Regular HSS?

The short version: standard high-speed steel bits get their hardness from heat treatment, but that hardness fades fast when friction pushes temperatures up. Cobalt changes the alloy itself so the bit keeps its edge at higher drilling temperatures.

Two grades dominate the shelves:

• M35 — contains about 5% cobalt, the most common all-around grade
• M42 — contains about 8% cobalt, with extra heat resistance for the toughest jobs; Bosch claims its M42 alloy delivers up to 10X the life of standard bits

You’ll spot these bits by markings like HSS-Co5 or HSS-Co8 stamped on the shank. If a bit has no cobalt marking at all, treat it as plain HSS — unmarked “cobalt” claims aren’t worth trusting.

When Should You Reach For Cobalt Bits?

Cobalt bits earn their keep on hard, abrasive metals where standard HSS goes limp. Bosch positions its cobalt lines for stainless steel, cast iron, titanium, light-gauge metal, and aluminum. Milwaukee’s Red Helix cobalt bits are sold from 1/16″ up to 1/2″ and are aimed at the same hard-metal work, plus PVC and wood in a pinch.

What To Drill With Cobalt Bits

• Stainless steel — the most common reason people upgrade
• Cast iron and titanium — both eat standard bits quickly
• Other hard or abrasive metals where heat buildup is the enemy

That doesn’t make cobalt the default choice for everything. For soft materials like plain mild steel, aluminum, or wood, standard HSS bits cost less and cut fine. Cobalt’s extra hardness mainly matters when the material fights back.

What To Look For In A Cobalt Bit

Not all cobalt bits are built the same, and the differences show up fast on tough metal. Three features matter most:

The split point. A 135-degree split point is the geometry standard on quality cobalt bits. Bosch builds a “no-skate” tip into its cobalt bits, and Milwaukee’s Red Helix line uses a 135° split point tip — both designs let the bit start cutting where you place it instead of skating across the surface. This is the feature that saves you from ruined workpieces and wandering holes.

The shank. On Bosch’s cobalt bits sized 3/16 inch and larger, a three-flat shank improves grip in the chuck so the bit doesn’t slip under load. Smaller bits skip this feature, so don’t expect it on the little ones.

The helix angle. Milwaukee’s Red Helix bits use a variable helix design with an enhanced tapered web, which helps clear chips and adds strength where the bit is thinnest.

If you’re comparing specific models for a purchase, our tested roundup of the best cobalt drill bits for metal breaks down the top options side by side.

Are Cobalt Bits Worth The Extra Cost?

For occasional home use on mild steel, the answer can honestly be no — standard HSS is cheaper and does the job. But if stainless steel, cast iron, or titanium show up in your projects with any regularity, cobalt bits pay for themselves by surviving jobs that would dull or destroy standard bits.

One honest caveat: cobalt bits are harder, which also makes them more brittle than standard HSS. They handle heat well, but they don’t love abuse — use steady pressure, let the bit do the cutting, and avoid excessive side loading.

Pricing for individual bits runs roughly $5 to $15 depending on size and brand, and sets offering a range of diameters cost more but spread the per-bit cost out. Match the bit size to the job, keep speeds moderate on stainless, and these bits will outlast several sets of standard HSS on the same work.

FAQs

Can cobalt drill bits be used on wood?

Yes, cobalt bits will drill through wood and PVC without issue, and Milwaukee lists both materials as suitable for its Red Helix cobalt line. The trade-off is that cobalt bits cost more than standard wood bits, so they’re not the economical choice when wood is all you drill. They shine when one bit needs to handle both metal and occasional softer materials.

How can I tell if a drill bit is really cobalt?

Look for a clear alloy marking such as HSS-Co5 or HSS-Co8 stamped on the shank, which indicates M35 or M42 cobalt content respectively. Unmarked bits should be treated as standard high-speed steel. Reputable brands like Bosch and Milwaukee mark their cobalt content clearly, so when in doubt, buy from a known manufacturer rather than a generic unbranded listing.

Do cobalt drill bits need to be used with cutting fluid?

Cobalt bits tolerate higher temperatures than standard HSS, but cutting fluid still helps. On stainless steel and other hard metals, a light oil or cutting fluid reduces friction, extends bit life, and produces cleaner holes. For occasional use, you can drill dry in a pinch, but the bit will run hotter and dull sooner than it would with proper lubrication.