There aren’t many materials strong enough to put holes in hardened steel. For that kind of strength, the only answer is cobalt alloy drill bits.
These powerful cobalt drill bits for cast iron, aluminum, and even stainless steel are made of a steel alloy of 5 percent to 8 percent cobalt. We researched dozens of cobalt drill bit sets before testing the following picks.
Read on to find out more about our shopping considerations and testing process. This guide will help you find the best cobalt drill bits for turning metal into Swiss cheese.
- BEST OVERALL: DeWalt Industrial Cobalt Alloy Steel Set
- RUNNER-UP: Irwin 29-Piece Cobalt Alloy Steel M35 Drill Bit Set
- BEST BANG FOR THE BUCK: Amoolo 13-Piece Cobalt Drill Bit Set
- UPGRADE PICK: Drill America Cobalt Jobber Drill Bit Set
- BEST M42: Bosch 14-Piece Cobalt M42 Drill Bit Set
- BEST FOR STAINLESS STEEL: Milwaukee 15-Piece Cobalt Red Helix Drill Bit Kit
- BEST METRIC: Stroton Metric M42 8% Cobalt Twist Drill Bits Set
- BEST STEP BITS: Milwaukee 3-Piece Cobalt Step Drill Bit Set
Before You Buy Cobalt Drill Bits
Before deciding to purchase a set of cobalt drill bits for metal, shoppers will want to make sure they know what they’re getting. While these bits can cut a variety of materials, they are specifically designed to cut through hard metals such as stainless steel, cast iron, hard steel, and even titanium. Because cobalt alloy bits are more expensive than conventional metal drill bits, they aren’t economical options for drilling materials like wood or masonry. Before making a purchase, shoppers will want to make sure they’re buying the right drill bits for the job.
In addition, be aware that drilling into hard metal requires a special technique to ensure that the bit cuts into the metal smoothly without overheating. Use a quality drilling lubricant with a high flash point. We used 3-In-One Multi-Purpose Oil for our tests. Also, drill at a slower speed with moderate downward pressure to avoid damaging expensive bits. The smallest bits can safely drill at about 3,000 rotations per minute (rpm), but larger bits should turn no faster than about 1,000 rpm.
How We Tested Cobalt Drill Bits
Machinists, mechanics, DIYers, and crafters value cobalt bits for their ability to drill hard materials and because they can be resharpened. We spent 12 hours testing these drill bit sets. First, we used a drill press to evaluate them for drilling ability in aluminum, cast iron, and stainless steel. Then we resharpened them before performing a second round of drilling tests. (For most products, we used a drill press for each set of holes; however, for two products, we used a drill press and a cordless drill, as noted above.)
For the first round of drilling evaluations, we selected the 1/16-inch, 3/16-inch, and ⅜-inch bits from each set. The test materials included scraps of .25 sheet aluminum, .133 cast-iron pipe, and .065 square tubular stainless steel. We calibrated the drill press rpm to match the bit size and material based on this chart and used 3-In-One Multi-Purpose Oil as a drilling lubricant. We drilled three holes in each of the test materials with every drill bit and then noted penetration speed (aggressiveness), cleanliness of the hole edges, and any noticeable changes from the first to the last hole.
After drilling the first round of test holes (or after the second round for some harder drill bits), we sharpened the ⅜-inch bits with a bench grinder. We held the cutting edge to the wheel for 5 seconds on each cutting edge, once on the coarse grinding wheel and once on the fine wheel, making sure to maintain the 135-degree original tip angle. To evaluate how well the bits responded to resharpening, we drilled another round of three test holes for each bit in the scrap steel.
We tested with an eye out for the best drill bits that might work especially well for specific metals, such as which ones may be best for stainless steel or best for cast iron. While the unique tips on the Milwaukee 15-piece cobalt drill bits proved especially effective at drilling in stainless steel, all of these drill bits would do well boring clean holes into a variety of metals. With that in mind, we assigned awards for each product based more on its features rather than on specific metal uses.
Our Top Picks
After researching more than 40 cobalt drill bit sets, we spent hours testing the following bits on aluminum, cast iron, and stainless steel. Read on to learn how they performed in testing and why we consider them to be some of the best cobalt drill bits around.
When drilling metal, some of the biggest headaches are bits that break, spin in the chuck, and bounce over the metal’s surface. DeWalt addresses all those issues with this set.
Picked as our best drill bit set, this high-grade cobalt and stainless steel enhance the durability of these drill bits, so users don’t need to worry about breaking a bit. A pilot point makes it much easier to get started and eliminates the need for a separate pilot hole. And DeWalt goes with a flat-sided shank to get rid of spinning issues. This 14-piece set includes sizes ranging from 1/16 inch to ⅜ inch.
In testing, the stepped split pilot point allowed the DeWalt cobalt metal drill bits to penetrate the metal quickly without slipping. They maintained a good level of sharpness through the first three holes, but the point was slightly less aggressive by the third hole.
Having two levels on the point made it more difficult to sharpen the bit accurately while maintaining the factory angle, but we managed to shape it up. The final test hole after sharpening came out smooth and clean. We also really liked the 3-flat shank that made these bits fast and easy to assemble into the drill chuck. For the price, these bits make a good all-purpose choice, especially for those who drill metal regularly.
- Number of bits: 14
- Sizes: 1/16 inch to ⅜ inch
- Cobalt value: M35
- 3 flat sides on the shank for more secure chucking
- Stepped split tip penetrates material more accurately than similar products
- Includes the most commonly used bit sizes for most drilling projects
- Ruggedly built carry case and clear lid with easy bit indexing
- Stepped split bit is more difficult to resharpen compared to similar drill bit sets
Get the DeWalt cobalt drill bits at Amazon, Ace Hardware, or Lowe’s.
Those in need of several bit sizes will want to check out this 29-piece set from Irwin. Sizes for these twist drill bits run from 1/16 inch to ½ inch in 1/64-inch increments. Each bit features a split-point top, which makes starting holes easier. The M35 alloy bits are made from an alloy of steel and 5 percent cobalt for longer life under tough drilling conditions.
As a lot of DIYers can attest, loose bits eventually become lost bits. Irwin knows that, so this set comes with a convenient carrying case that securely indexes all 29 bits into three separate cartridges that fit neatly into a durable and portable rubber molded case.
The Irwin M35 drill bits performed well before and after sharpening—in fact, the bit had barely dulled after the first three holes. With or without a center punch to premark the hole locations, these bits drilled smooth, clean holes. Also, the split point was easy to line up at the proper angle to sharpen on the grinder.
We really liked the bit case for organized storage, although the combined weight of the metal case and 29 bits was heavy—probably best for workshop use. With so many sizes to choose from in 1/64-inch increments, this set would be a great pick for those who need precision drilling for a variety of projects. On the other hand, its premium price may not be worth it for those who would need these bits only for occasional use.
- Number of bits: 29
- Sizes: 1/16 inch to ½ inch
- Cobalt value: M35
- Split point is easy to resharpen to extend the working life of the bit
- M35 cobalt alloy is compatible with most hard and soft materials
- 29-piece set offers more incremental sizes for precision drilling projects
- Includes a heavy-duty steel carrying case with a tap-and-drill selection chart
- Premium price compared to other cobalt drill sets on the market
- Heavy carrying case is not ideal for transporting to jobs
Get the Irwin cobalt drill bit set at Amazon, Acme Tools, or Tool Barn.
This 13-piece set from Amoolo comes in at a fraction of the price of other cobalt drill bit sets. This set is durable, with 5 percent cobalt steel alloy, though not as strong as M42 bits, which contain 8 percent alloy. Using a lubricant or cooling water can help extend the life of these bits. Their split-point tips prevent walking and make starting holes easier. Ranging in size from 1/16 inch to ¼ inch, these bits come in a plastic carrying case with labeled sizes.
The Amoolo cobalt drill bits performed as well as some of the top name brands in our tests but cost a fraction of the price. They drilled smooth, clean holes, and the 135-degree split point was easy to align with the bench grinder for sharpening. It bears mentioning, however, that the kit only includes smaller bit sizes in 1/16-inch increments, which makes it ideal for crafting and detailed drilling.
The only downside we found was the flimsy plastic case and foam bit holder: They felt more like shipping materials than parts of a protective carrying case. Still, functionally speaking, we doubt that anyone would know the difference if we replaced some of their Irwin cobalt drill bits with these.
- Number of bits: 13
- Sizes: 1/16 inch to ¼ inch
- Cobalt value: M35
- Compared to top name brands, offers a budget-friendly price point for heavy-duty drill bits
- Bit sizes are given in both fractions of an inch and in millimeters
- Includes 13 bits in 1/64-inch size increments for precision drilling
- Split point is easy to resharpen for a longer working life
- Flimsy plastic and foam carrying case compared to those offered by other brands
Get the Amoolo cobalt drill bits at Amazon.
This set of premium cobalt drill bits from Drill America features 29 pieces that range in size from 1/16 inch to ½ inch in 1/64-inch increments. The gold finish acts as a built-in lubricant to keep heat levels down, making it the strongest drill bit for drilling through metal easier and extending the life of the bit. Each bit is made from high-grade M42 cobalt stainless steel alloy. A split point quickly penetrates hard metals without the need for a pilot hole.
Working with the Drill America M42 drill bit was almost an identical experience to working with the Irwin drill bit set, but this set is made of tougher metal and provides easier access to all of the bits at once. Both sets offer the same size assortment, the same round shank, and 135-degree split-point construction. Drill America’s bits remained noticeably sharper after the first three test holes, so we drilled a second set of three holes before sharpening. Sharpening took slightly longer, but the split point made it easy to align them with the grinder.
The round plastic carry case was more compact and lightweight than the Irwin case and featured a watertight threaded cover, but reading the bit size labels was more difficult. This could be a nice set to keep in the shop or for carrying to project sites.
- Number of bits: 29
- Sizes: 1/16 inch to ½ inch
- Cobalt value: M42
- M42 cobalt alloy steel bits work harder and last longer than M35 bits
- Split-point tips can be resharpened for a longer working life
- Kit includes 29 bits and 1/64-inch incremental sizes for precision drilling
- Unique round carry case offers fast access to different bit sizes
- Bit sizes on the carry case rim are not easily visible
Get the Drill America cobalt drill bits at Amazon or DrillsAndCutters.com.
With its M42 drill bits, this set from Bosch is ready to take on the hardest metals. The 8 percent cobalt alloy is more durable than what’s used for M35 cobalt drill bits, giving it longer shelf life. This set’s other features also make drilling through metal a breeze. A split-point tip penetrates metal easily, while a flat shank prevents slipping in the chuck. These Bosch bits have thicker threading than most spiral drill bits, a design that’s meant to remove material more efficiently and decrease the amount of time it takes to drill through metal. This set includes 14 pieces, with sizes ranging from 1/16 inch to ½ inch.
The Bosch cobalt drill bits offer a unique combination of structural features and extra-hard M42 alloy that make them a pleasure to work with. To test this product, we used a cordless drill and a drill press to highlight the difference between precision drill press work and handheld drilling. The cordless drill mostly worked well, but its variable-speed trigger made it more difficult to maintain a slow, precise speed for drilling steel.
Overall though, we really liked the split-point tip and 3-flat shank for secure chucking, smooth drilling, and easy sharpening. As with our other M42 test bits, these held their edge well enough to drill a second set of test holes with the drill press before sharpening. Sharpening was also easy thanks to the split point. For drilling hard, brittle cast iron, the extra control afforded by the design of these bits was especially helpful.
- Number of bits: 14
- Sizes: 1/16 inch to ½ inch
- Cobalt value: M42
- Split-point bits are easy to sharpen for an extended working life
- 3 flat sides on the shank eliminate slipping in the drill chuck
- M42 cobalt alloy lasts longer and works harder than M35 alloy
- Kit includes the most popular drill bit sizes for general-purpose drilling
- Bit size labels on the carry case are extremely hard to read
Get the Bosch cobalt drill bits at Amazon, The Home Depot, or Lowe’s.
Drilling into hard stainless steel with a poorly designed bit leads to bit breakage, bit shafts spinning in the drill chuck, or the tip simply not penetrating the surface. The Milwaukee Red Helix cobalt drill bit set avoids these issues.
Made with M35 cobalt alloy, this Milwaukee cobalt drill bit set is tough enough to penetrate stainless steel without breaking. A stepped split-point tip eliminates the need for a center punch or pilot hole. And the 3-flat shank puts an end to loose bits spinning inside the chuck. This 15-piece set includes sizes ranging from 1/16 inch to ⅜ inch. These bits are compatible with all twist-drilling applications.
The Milwaukee cobalt drill bit set exceeded our expectations in the stainless steel drilling test. While most of the other bits did a pretty good job, the Milwaukee bits bit into the stainless steel noticeably faster. The slightly elevated point, which is shorter and narrower than DeWalt’s, seemed to find a sweet spot that then allowed the rest of the cutting edge to follow.
The raised center point didn’t get in the way when we sharpened the edges of the bit point, but sharpening the center of the point was more challenging. However, we found that these durable bits, housed within their well-built hard plastic case, would make a great addition to a workshop.
- Number of bits: 15
- Sizes: 1/16 inch to ⅜ inch
- Cobalt value: M35
- 3-flat shanks chuck more securely in the drill than round shanks
- Stepped split-point bits penetrate material more precisely than regular split points
- Kit includes the most popular bit sizes for general-purpose drilling
- Heavy-duty carry case includes convenient, easy-to-read size labels for each drill bit
- Stepped split-point bits are more difficult to sharpen than regular split points
Get the Milwaukee cobalt Red Helix drill bits at The Home Depot, Northern Tool + Equipment, or Acme Tools.
It takes a tough bit to drill through hard metals like steel and bronze, but drill bits like these from Stroton are up to the task. Stroton uses what it calls a three-step design with this drill bit. Borrowing from step-bit technology, the tip of the bit is composed of three separate steps that help drive the bit through hard metals. This 19-piece metric set features sizes ranging from 1 millimeter to 10 millimeters.
The Stroton cobalt drill bits featured a round shank with a low-profile stepped split point. They performed smoothly with or without center-punch starter guides. Unlike the more exaggerated pilot-style stepped points found on the DeWalt and Milwaukee bits that we tested, this design only stepped up a total of about 0.5 millimeters above the shoulders of the bit point, despite having more steps.
The effect was a combination of quick bite into the material and smooth transition to the full width of the bit. The M42 alloy construction allowed these bits to hold up longer than those made of M35, but it took a bit more effort to sharpen them due to the material’s increased hardness. We didn’t love the cheap plastic case, but it worked, and the metric size labels were easy to read.
- Number of bits: 19
- Sizes: 1 millimeter to 10 millimeters
- Cobalt value: M42
- Includes 19 drill bits in ½-millimeter increments for precision drilling
- M42 alloy bits stay sharp longer than M35 bits under tough drilling conditions
- Stepped split points can be resharpened to extend the drill bit’s working life
- Flimsy plastic carry case may not hold up over long-term use
Get the Stroton cobalt drill bits at Amazon.
Step drill bits offer the advantage of fast, clean precision drilling into thin metals without changing bits. Each of this set of three cobalt step drill bits is designed and engineered to drill up to 1,000 holes into 14-gauge steel. They feature a rapid strike tip for faster starting, elongated dual flutes to reduce heat buildup, and smaller step gradients for smoother drilling.
To help ensure precise drilling, hole sizes are laser engraved inside the flutes. The bit shanks feature a 3-flat design to eliminate slippage in the drill chuck. They offer outstanding performance in cordless drills on low speed for stainless steel or high speed for mild steel.
The kit includes #1, #4, and #9 step bits. The #1 bit drills from ⅛-inch to ½-inch holes, with step increments of 1/32 inch. The #4 bit makes holes 3/16 inch to ⅞ inch, in 1/16-inch increments. The #9 bit drills ⅞- to 1⅛-inch holes in 1/16-inch increments.
Since the manufacturer recommends these bits for cordless drilling, we tested the Milwaukee step bits twice, first in the drill press and then in a handheld cordless drill. They drilled fast and clean as billed. Then we tested the step bit’s unique ability to enlarge existing holes—a task that is nearly impossible to do cleanly with conventional twist bits. We clamped an old steel electrical junction box to the workbench and used the #9 step bit in a cordless drill to widen the punch-out holes from ½ inch to ⅞ inch. The resulting hole was perfectly shaped, clean, and smooth, with no burs.
Because the step bit’s cutting edges run from top to bottom along the edges of the flutes, instead of at the tip only like twist bits, we approached resharpening differently. We clamped the bit in a vice and used an angle grinder to touch up the cutting edges. It worked fine, but we had to be extra cautious not to damage the size markings.
- Number of bits: 3
- Sizes: 1/16 inch to 1 ⅛ inch
- Cobalt value: M35
- Includes 3 step bits sized in 1/32-inch and 1/16-inch increments for precision drilling
- 3-flat shanks that will not slip in the drill chuck
- Elongated dual-flute design resists heat buildup for smoother drilling operation
- Product is compatible with sheet steel up to 14-gauge thickness
- Has a specialized design that will only work with sheet metals
Get the Milwaukee step cobalt drill bits at The Home Depot, Acme Tools, Grainger, or ToolUp.
What to Consider When Choosing the Best Cobalt Drill Bits
DIYers will want to consider several features, such as drill-bit type, size, and cobalt value, ahead of purchase. So before they grab the first set of cobalt drill bits they can find, shoppers will want to be sure to take into account exactly what the project requires.
There are four types of cobalt drill bits, with each type serving a specific purpose. Understanding the right application for each bit type is essential.
- Twist. Twist bits are general-purpose drill bits and are capable of drilling a variety of different materials. They have angled grooves that spiral around the drill shaft. The edges of these angles are sharp, allowing the bit to burrow into the material. Cobalt twist bits are strong enough to bore into hard metals quickly. They come in a wide variety of sizes, with sets including up to 30 pieces.
- Countersink. Countersink drill bits create shallow holes that allow the head of a fastener to sit flush with the material and are angled to match the tapered head of the fastener. Cobalt countersink bits will create countersink holes in hard metals. Unlike twist drill bits, which include self-piloting tips, countersink bits require an existing hole to drill into a material. To drill countersink holes, twist bits are needed to drill the initial hole, then countersink drill bits are used to create the countersink holes.
- Counterbore. Counterbore drill bits create holes that allow the head of a fastener to sit below the material’s surface. Unlike countersink bits, which create an angled hole for fasteners with angled heads, counterbore drill bits create a larger hole at a shallower depth. A counterbored hole creates a flat ridge on which the head of the fastener can rest.
- Cobalt step. Cobalt step drill bits are designed to drill holes into sheet metal. With its cone-like shape, a step bit enlarges the hole as it moves through the sheet metal, allowing users to regulate a hole’s diameter. A step bit works with up to ¼-inch-thick sheet metal. Those looking to drill at shallow depths through sheet metal will want to consider using a step bit.
Most twist bits come in diameters ranging from 1/16 inch to ½ inch, creating holes corresponding to the diameter. Step bits, which are shaped more like a cone, can drill holes ranging in diameter from about ⅛ inch to ½ inch, with a maximum depth of ¼ inch. For deeper holes, look to purchase a twist bit.
Size also affects wear, and length negatively impacts durability. Long drill bits are not as durable as shorter bits due to the amount of torque needed to rotate longer bits. Shorter bits also resist twisting or spinning in the drill chuck better.
Cobalt drill bits consist of steel with a small percentage of cobalt—the higher the percentage of cobalt, the more heat-resistant and durable the drill bits will be. The amount of cobalt in a drill bit varies. An M35-grade cobalt bit contains 5 percent cobalt, while an M42-grade cobalt bit contains 8 percent. The higher the grade, the more expensive the bit.
When attempting to drill through a hard, smooth surface, having the right tip is crucial. Most cobalt drill bits have tips with stepped and split points that bite into the metal, which prevent the bit from sliding along the smooth surface.
The drill-bit shank is the part that fastens into the drill chuck—the part of the drill that grips and turns the bit. Shanks may be round (also known as “flat”) or shaped for improved grip. Round shanks work well in keyed chucks. In keyless chucks, like those on cordless drills, shaped shanks offer better grip and eliminate the bit slipping inside the chuck. The most popular-shaped drill-bit shanks include 3-flat, which have three flat sides ground into an otherwise round shank, and six-sided hex shanks.
Tips for Buying and Using Cobalt Drill Bits
Before buying or using a cobalt drill bit, it’s important to consider a few tips.
- Don’t throw away dull drill bits. Instead, sharpen them with a grinder to restore their sharp edges.
- Only use cobalt bits for drilling holes in metal, as the bits are too powerful for wood and other materials.
- Drilling through steel, cast iron, and other metals produces tiny shards that can end up in skin or eyes, so make sure to wear protective gloves and safety glasses when working with cobalt drill bits.
Still wondering if cobalt bits are the best tool for the job? Read on for answers to the most common questions about cobalt drill bits.
Q. Can cobalt drill bits be sharpened?
While cobalt drill bits will hold up better against heat than other drill bits, they will need to be sharpened from time to time. Sharpen dull cobalt drill bits using a bench grinder.
Q. Are cobalt or titanium drill bits better?
Titanium drill bits are durable and will hold up much longer than standard high-speed steel drill bits, but they are not as strong as cobalt alloy, which will drill through hard metals, including titanium.
Q. What are the hardest drill bits?
M42 cobalt drill bits, which have 8 percent cobalt, are the hardest drill bits available.
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