What Are Cobalt Drill Bits? | Hard-Metal Powerhouse

If you’ve ever watched a standard bit smoke and dull while drilling into stainless steel, you’ve felt the exact problem cobalt bits solve. Cobalt drill bits are high-speed steel (HSS) with cobalt mixed into the alloy, which lets them hold up to the intense heat that hard metals generate. Milwaukee’s RED HELIX line is the most visible example on the market, and its specs show what makes this category different from the black oxide bits in most garage starter kits.

What Makes Cobalt Bits Different From Regular HSS?

The short answer is the alloy itself. Cobalt drill bits add roughly 8% cobalt to the high-speed steel formula, which strengthens the material and improves its heat resistance. That matters because drilling stainless steel creates friction fast, and a standard HSS bit loses its temper once the edge gets hot. A cobalt bit keeps cutting.

Milwaukee’s RED HELIX cobalt bits show the other engineering details that separate good cobalt bits from cheap ones. First, the 135° split point tip delivers a precise start that prevents walking across the work surface. Second, the variable helix geometry — starting at a 35° angle and tapering to 15° — is designed to move chips out of the hole faster and reduce heat buildup. Third, some sizes include a QUADEDGE TIP and an enhanced tapered web for extra flute durability.

Milwaukee rates these bits for wood, stainless steel, metal, plastic, and PVC, and claims up to 15 times the life of black oxide drill bits. That comparison is product-specific, not a universal rule, but it signals the durability gap between entry-level bits and cobalt alloys.

Are Cobalt Bits Good For Stainless Steel?

Yes. Stainless steel is the primary target for cobalt drill bits, and the material’s hardness is exactly why you need the extra heat resistance. The 135° split point on Milwaukee’s bits is the feature that matters most for hard metals — it keeps the bit from sliding across the surface when you start the hole, which is the most common beginner failure drilling stainless.

One honest caveat: cobalt bits are durable HSS, not carbide. They will outperform black oxide and standard HSS on hard metals, but they are not a universal solution for every abrasive material. For masonry or tile, you still want the specialized bits designed for those jobs.

What Sizes And Sets Does Milwaukee Offer?

The RED HELIX family spans individual bits and full sets, and the shank style changes depending on the size you pick. That detail matters more than most shoppers expect — a 3/8″ reduced 3-flat shank won’t seat the same way as a round shank in every chuck.

Before you buy a single size, verify the exact model page for the diameter, shank, and length you need — those specs vary by size, and the wrong shank type can make a bit unusable in your drill. If you’re building out a kit or replacing a worn set, our tested roundup of the best cobalt drill bits for metal compares the top options side by side.

How Do You Use Cobalt Bits Without Breaking Them?

Start with a pilot hole for anything larger than 1/4″, and run the drill at a slower speed than you’d use for wood. High speed plus hard metal equals heat, and heat is the enemy of any cutting edge — even a cobalt one. Use cutting fluid or a light oil on stainless steel to keep the temperature down and extend the bit’s life.

Drill with steady, firm pressure. Let the bit do the cutting instead of pushing hard enough to stall the drill. The split point will grab the surface and hold its position, so you don’t need excessive force to keep it centered. When the hole breaks through the far side, ease off the pressure to avoid catching the bit and snapping it.