So you need to buy a drill stem or some core bits, and you're not sure where to start. I get it. A few years ago, I was in the same spot. I manage purchasing for a mid-sized civil engineering firm—processing about 80 equipment orders a year. When my operations lead asked me to source replacement drill rods and bits, I had to learn fast. Here are the questions I wish I'd had answered from the start.
1. What's the difference between a 'drill stem' and a 'drill rod'?
Technically speaking? Almost nothing. In the field, people use them interchangeably. A drill stem (or drill rod) is the hollow, threaded pipe that transmits rotation and torque from the drill rig down to the bit. If I'm being precise, 'drill stem' is the whole assembly, but if you search for well drill rod or 2 7 8 drill stem for sale, you're looking at the same kind of product. For ordering, just focus on the thread type and the outer diameter (e.g., 2-7/8 inch). That's what matters for compatibility with your rig.
2. I see 'diamond core cutting bit'—is that overkill for my job?
Honestly? It depends on what you're cutting. A diamond core cutting bit is the gold standard if you need a clean, precise hole through reinforced concrete or hard stone. If you're just going through asphalt or soft shale, a standard carbide-tooth bit will do the job for way less money. But here's the kicker: I've seen crews burn through three carbide bits trying to get through one slab of granite. A diamond bit, even though it costs more upfront, saved us a ton of downtime. So, no, it's not overkill if you're dealing with hard material. It's just a different tool for a specific job.
3. What size core drill bit do I actually need? 6-inch? 4-inch?
This gets into logistics territory, which isn't my expertise. What I can tell you from a purchasing perspective is: don't guess. The size—whether you need a 6 inch core drill bit or a core drill bit 4—is determined by the diameter of the pipe or cable you're running through it. Your project engineer should have this spec'd out. If they say, 'Just get a 6-inch,' ask why. A 6-inch bit makes a bigger hole, which means more concrete to dispose of and potentially more vibration damage. A 4-inch is usually fine for single cables or small pipes.
4. What are the best bits for drilling granite?
Assuming you're not blasting, the answer is a diamond-tipped bit, specifically a diamond impregnated core bit. Standard steel bits won't even scratch it. For granite, you need a bit where the diamond segments are embedded into the matrix of the bit crown. Also, don't skimp on the water flow. Dry drilling granite with a diamond bit will cook it in about 30 seconds. In our last project, we tried a cheap 'multi-material' bit on a piece of granite countertop offcut. It lasted about 15 seconds before it was a smooth, useless ring. We then rented a proper diamond core bit and it cut through like butter.
5. How much should I budget for a 2-7/8 drill stem?
Pricing is volatile because it depends on steel costs and thread type, but here is a realistic ballpark from my Q4 2024 data. Based on publicly listed prices from major industrial supply houses as of October 2024, a 10-foot section of new 2-7/8 IF (Internal Flush) drill rod typically runs between $250 and $450. Premium brands or thicker wall options (for deeper drilling) go higher. Used or 're-run' drill stem can be 30-50% cheaper, but you risk hidden fatigue cracks.
Verify current pricing at your supplier as rates may have changed. Don't forget to factor in shipping—a 20-foot drill rod is heavy and freight costs are real.
6. Can I use the same bit for concrete and granite?
Not if you want it to last. This is a classic rookie mistake. A core drill bit 4 designed for general concrete has a softer bond that wears away to expose fresh diamonds. If you use it on hard granite, the bond won't wear fast enough, and the diamonds will get glazed over (polished smooth). You'll get very slow drilling and eventually a ruined bit. If you use a granite-specific bit (with a softer bond) on concrete, it will wear out too fast. You need the right bit for the material.
7. I need a 2 7 8 drill stem for sale—should I buy new or used?
I told my operations manager I wanted to save money and buy used for a shallow drilling job. He looked at me and said, 'You're signing up for the inspection cost.' He was right. If I remember correctly, we found a good deal on a lot of used stems. The price was great. But then we had to pay a third-party inspector to check every single rod for straightness and thread wear. The cost and time killed the savings. Plus, if one rod fails 50 feet down, the whole string is stuck. For critical work or deep holes, buy new. For shallow, low-risk jobs, used can work—but budget for a proper inspection. That's my rule now.
That said, for a one-off job, the bottom line is simpler: buy the right tool for the material. If you're drilling granite, spend on the diamond bit. It's a pain to explain to your boss why you need a $400 bit instead of a $50 one, but it's way worse to explain why the crew is sitting idle.
