Core Drill Bit Buying Guide: Four Scenarios, Four Different Answers

Ask five people what the best drill bit is and you'll get five confident answers. At least four of them will be wrong for your job.

I'm the office administrator for a 180-person building services company. I manage about $420,000 a year in maintenance and job-site consumables across nine vendors—everything from shop towels to the bits our technicians put holes in things with. I'm not a driller. I'm the person who gets a call at 4:30 on a Friday because the crew ran out of 7/16" bits and there's a Saturday shift.

After five years of buying these things, I've noticed that almost every bit request falls into one of four scenarios: concrete anchor holes, tile and stone, large penetrations, and steel. The right answer is completely different in each one. Guessing wrong is how you spend four times what you needed to.

Scene 1: Small Holes in Concrete or Masonry (1/4" to 7/16")

This is the bread-and-butter case. Anchor holes for wedge anchors, sleeve anchors, handrails, shelving, pipe straps. A 7/16" bit is about 11.1 mm and comes up constantly because it's the hole size a lot of mid-weight anchor hardware expects. A 1/4" bit comes up even more.

Here's the counterintuitive part. Most people assume diamond is the premium choice everywhere. For small anchor holes in concrete, it usually isn't. Carbide-tipped SDS-plus bits drill these faster, cost a fraction as much, and don't need water or a vacuum setup. You will burn through them—hard concrete eats carbide—but at roughly $8–20 a bit depending on length and brand, that's a consumable, not a capital decision.

Diamond drill bits for concrete at small diameters are slow, need cooling, and cost several times more per bit. They make sense if you're drilling hundreds of holes on the same site, or if you're in engineered concrete where a blowout is expensive. For twenty anchor holes at a school, they're overkill.

One thing I've learned the hard way: I don't decide the hole size. The anchor manufacturer does, and the spec sheet is not a suggestion. If a tech asks for a 7/16" bit and I hand them a 1/2" because that's what was in stock, that's a loose anchor and a callback. Ask for the spec, or ask for the anchor part number and look it up.

I don't have hard data on how many holes a carbide bit should reasonably drill. What I can say anecdotally is that our crews seem to get somewhere between 30 and 60 holes out of one in older, harder concrete, and considerably more in newer pours.

Scene 2: Small Holes in Tile, Stone, or Glass (1/4" Diamond)

Here diamond is the right answer and there's no real alternative. Carbide will skate across glazed tile, chip porcelain, and shatter glass. A 1/4" diamond drill bit grinds its way through instead of cutting, which is why it feels slow and why it fails the moment you lean on it.

Three things matter more than brand at this size: speed, cooling, and whether the bit is actually rated for the material. Most 1/4" diamond drill bits want low RPM—under 1,000 for glass, closer to 1,500–2,500 for porcelain depending on the bit—plus continuous water or a coolant slurry. Drill dry and you'll glaze the diamond, which is a polite way of saying you melted it.

Also worth knowing: "diamond bit" on a product page can mean at least three different tools. A thin continuous-rim bit for tile. A thicker sintered bit for stone. A small core bit for concrete. Buying the wrong one is a $15 mistake that costs you a day of someone's labor.

Scene 3: Big Holes Through Concrete (2" to 8" Core Bits)

This is where most buyers—me included, once—make an expensive mistake. An 8 core drill bit sounds like something you buy. It's usually something you rent, or a service you hire.

A wet diamond core bit at 8" is serious tooling. The bit alone was quoted in the mid-hundreds the last time I checked. That's the cheap part. You also need a rig with enough torque, a vacuum anchor or a stand bolted to the slab, a water feed, and a way to contain the slurry before it runs across a finished floor. Then consider the hole itself: it's probably for a duct or a conduit, which means it's a one-time cut in one specific spot.

The upside of owning the setup was being able to drill whenever we wanted. The risk was buying a $2,000 rig that sits in the corner eleven months a year while the seals harden and the bits sit there. I kept asking myself whether the convenience was worth that. Eventually I stopped pretending the answer was yes.

For anything above about 4 inches, renting the rig and hiring a concrete cutting crew for a day has come in at a fraction of the cost of buying. And when they misalign a cut, it's their problem to fix, not mine to explain to a project manager.

Scene 4: Holes in Steel Plate and Structural Metal

Nothing from the concrete advice transfers here. Diamond is the wrong tool for steel, full stop. Diamond doesn't tolerate heat, and cutting steel generates a lot of it. At high temperatures diamond starts converting to graphite and the edge is gone—you've paid a premium for a tool that dulls faster than the cheap one. Diamond also reacts with iron at cutting temperatures, which is why you'll never see it recommended for steel in any serious tooling catalog.

What you want instead is an annular cutter, often sold under the name core drill bits for metal, run in a magnetic drill press. Annular cutters cut a ring and eject a slug, so you're removing far less material than a twist drill would. For anything 3/4" and up in plate steel, that's the difference between a clean hole in thirty seconds and a smoked bit in five minutes. You'll also need cutting fluid. Not optional. The fluid is doing as much work as the cutter.

Bimetal hole saws still have a place: thin sheet, mixed materials, low volume, tight budget. They're cheap and they work fine. They also die fast in thick plate, and that's a lesson I learned the expensive way.

Back in 2022 we had a job drilling 3/4" plate for a handrail retrofit. I ordered bimetal hole saws because that's what the crew asked for and they were in stock. Two weeks in, we'd spent more on saws than a set of annular cutters would have cost up front, and the crew was still fighting chatter and burned edges. Looking back, I should have asked what they were actually drilling through. At the time I didn't know enough to ask, which is exactly the problem with ordering tools from a product listing.

How to Tell Which Scenario You're In

Three questions, in this order:

1. What's the material? Concrete and masonry, tile and stone, steel, or something mixed. Getting this right eliminates most of the wrong answers immediately.
2. What's the hole diameter and depth? Under half an inch, in the middle, or something you'd measure in inches of core. Diameter drives the tool class more than any other single factor.
3. Is this recurring or one-time? A facility with twenty identical anchor points a month justifies buying. A single 6" penetration in a leased building does not.

If you're stuck between two scenarios, start smaller and cheaper, then escalate. A carbide bit that turns out to be slightly wrong costs you twelve dollars. A diamond core bit that turns out to be slightly wrong costs you a few hundred and probably a delay on someone else's schedule.

One more thing, because it took me a while to appreciate it. The suppliers who've kept my business are the ones who told me when something wasn't their product. The rep who said "we don't stock wet core bits above 6 inches—you want a concrete cutting outfit for that" earned my trust on everything else. The ones who answer "yeah, we can get that" to every question are the ones whose orders I now double-check before anything goes to a job site.

Price ranges in this piece come from quotes we collected in late 2024 and early 2025. Carbide and diamond pricing moves with raw material costs, and the right bit still depends on your concrete, your drill, and the anchor spec. Verify current numbers before you budget anything.