Best cobalt drill bit sets

This is the set I'd point most people to first. It holds 29 bits from 1/16 to 1/2 in., stepping up 1/64 in. at a time. That's every fractional size in the range, so the size a fastener or a print calls for is in the case.

The alloy is M35, which IRWIN lists as 5% cobalt. IRWIN says the cobalt is there for higher heat and abrasion resistance. The other makers here pitch cobalt for stainless and other hard metals.

Every bit has a 135° split point. IRWIN says it's there to minimize walk, so the tip stays on your mark instead of skating across smooth steel.

IRWIN also lists heavy-duty web construction. The web is the solid core between the flutes, and IRWIN says the heavier web is for strength and durability.

Two things aren't listed. The Amazon listing doesn't say whether the bigger bits have flats on the shank, and IRWIN's own site was down for maintenance on Oct 19, so the maker’s page couldn’t settle it. If bits spin in your chuck, Bosch lists three-flat shanks.

Against Drill America's M42 set, this one has less cobalt but lists a split point on every bit. Drill America doesn't list a point for its M42 set. My call: for mixed steel work, the stated split point is worth more day to day.

Run the big bits slow. In stainless, Norseman's speed chart works out to about 230 to 380 RPM for the 1/2 in. bit. In mild steel, the 1/4 in. bit runs about 1,220 to 1,680 RPM. The full speed table is further down.

When I read Amazon's data on Oct 19, this set was new, in stock and sold by Amazon.com.

Drill America describes cobalt steel as high-speed steel with more cobalt, for better performance in harder metals such as stainless steel and nickel alloys. This set uses M42, the higher-cobalt grade of the two you'll see on listings.

Drill America doesn't print a cobalt percent on this listing. For reference, Bosch lists its M42 at 8% cobalt and IRWIN lists its M35 at 5%. That gap is the whole M35 vs M42 question, covered in its own section below.

The size run matches the IRWIN: 29 bits, 1/16 to 1/2 in., by 64ths. So you're not giving up any sizes for the higher-cobalt alloy.

The bits have round shanks. Drill America says that lets them work in a wide variety of tool-holding systems. The flip side is grip: Drill America puts three flats on its stepped point set to stop spinning, and this set doesn't have them.

The gold color is gold oxide. Drill America calls it a thinner surface treatment than black oxide, used mainly to identify cobalt tools, with performance similar to uncoated bits. So the color tells you what it is, not how it cuts.

Drill America notes that the spiral flutes lift chips up and out of the cut in the normal right-hand cut direction, to reduce clogging. The set ships in a metal case.

My call: if most of your holes are in stainless, this is the set I'd buy. Pair it with the slow speeds in the chart below. Stainless wants less than half the speed of mild steel.

Drill America's own product pages need a distributor login, so these specs come from the Amazon listing. It was new, in stock and sold by Amazon.com on Oct 19.

Bosch lists these sets for rotary drills/drivers with three-jaw chucks. Bits 3/16 in. and larger have a three-flat shank, which Bosch says gives better grip.

The alloy is M42 with 8% cobalt, per Bosch. Bosch says it gives 10 times the life of its standard bits, though it doesn't say which bits it compared against. It lists stainless, cast iron, titanium, light-gauge metal and aluminum as the targets.

Bits 1/8 in. and larger have split points. Bosch says they start with no skating, so you can skip the center punch. The tips are surface-hardened, and the thick web-helix design adds stability in tough work, per Bosch.

The size list is where this set differs. Its 21 bits cover 16 sizes, with two each of 1/16, 5/64, 1/8, 3/16 and 1/4 in. My read: spares on the small sizes are the useful kind of extra, since a 1/16 in. bit is the easiest one to snap.

What you give up is the in-between steps. Above 1/4 in., you get only 5/16, 3/8 and 1/2 in. If you drill for bolts and need a size like 17/64 or 25/64 in., a 29-piece set has it and this one doesn't.

The CO14B is the smaller version: 14 bits, 13 sizes, with two 1/8 in. bits. It's listed here as a second option for a truck kit or a toolbag drawer.

Bosch's own page lists the CO14, CO21 and CO21B contents shown in the size chart below. The B models are the ones linked here, and the CO21B comes in a plastic case.

My call: if bits slipping in a cordless chuck is your problem, this is the set that fixes it. Both versions were new, in stock and sold by Amazon.com on Oct 19.

DeWalt says these industrial cobalt alloy bits are designed for maximum speed and life in stainless steel and other hard metals. It names stainless, angle iron and I-beams as the common uses.

The tip is the reason to pick this set. DeWalt's Pilot Point with a split tip starts on contact and doesn't walk. DeWalt also says it reduces lock-up on breakthrough. That's the moment the bit exits the far side and wants to grab.

My read: on hanger and support work, a bit built to reduce that grab is worth more than a few extra sizes.

The case is part of the pitch. It's DeWalt's ToughCase+ small bulk storage with a clear lid, a clip latch and a bit bar that lets you pull bits out and arrange them. It fits inside the small and medium ToughCase+ organizers, which are sold separately.

Here's what DeWalt doesn't list. Its page gives 14 pieces from 1/16 to 1/2 in. but not each size, and it doesn't give a cobalt grade or percent. The warranty field reads "Warranty information currently unavailable."

So compare this set on its point, not its alloy. If you need a known grade, the IRWIN (M35, 5%) and Bosch (M42, 8%) sets state theirs.

Speed still matters with a Pilot Point. In mild steel, Norseman's chart works out to about 610 to 840 RPM for a 1/2 in. bit. In stainless, drop to 230 to 380 RPM for the same bit.

My read: this is the structural steel set. For a mix of sizes in sheet and tube, a 29-piece set will cover more of the holes you drill.

Amazon also sells a five-pack of this set. I linked the single set, which was new, in stock and sold by Amazon.com on Oct 19.

This is Drill America's GSC series, a gold stepped point cobalt bit. Drill America says the stepped point lets the set work as an enlarger for existing holes as well as for new, smoother holes.

That makes it the set for a job like opening a 1/4 in. hole in a bracket to 5/16 in. Drill America lists acrylic, steel, brass and other hardened metals as the materials.

Drill America claims these bits start easier, drill faster, last longer and run cooler than standard drill bits. It doesn't say what it tested against, so read that as the maker's pitch.

The tip is a 135° split point. Shanks 3/16 in. and larger have three flats to prevent spinning, and 11/64 in. and smaller stay round. The bits are jobber length with a gold oxide finish.

The size list is printed in full: every 64th from 1/16 to 1/2 in., 29 bits in all. That's the same coverage as the IRWIN and the Drill America M42 set.

When you enlarge a hole, set the speed for the new size, not the old one. Taking a hole out to 5/16 in. in mild steel works out to about 980 to 1,340 RPM from Norseman's chart, slower than the 1/4 in. bit that drilled it.

The one gap is the alloy grade. The listing says cobalt but not M35 or M42, so you can't compare it on cobalt percent. Pick it for the point and the shanks.

Drill America has supplied industrial and contractor cutting tools since 1923, per the listing. Its site needs a distributor login, so these specs are from Amazon.

It was new, in stock and sold by Amazon.com on Oct 19. My call: this is a second set for most people, after a general 29-piece set.