What is drill rod? Grades, sizes and what it's used for
In this guide
Drill rod is round tool steel bar, precision ground to a tight diameter and sold soft so you can machine it and then harden it. McMaster-Carr sells it as "tight-tolerance" tool steel rod, ready for turning in a lathe.
This guide is part of our drilling hub. For how steel behaves when you cut and drill it, see our steel page.
What drill rod is (and isn't)
- It is tool steel in a ground round bar. The grinding makes it round, straight and exact in size.
- It isn't a drill bit. You can make tools from it, but it comes as plain, uncut bar.
- It isn't the "drill rods" used in mining and well drilling. Those are threaded steel tubes that connect a drill rig to the bit deep in the ground. Boart Longyear, for example, sells coring rods with different thread types for deep holes.
Grades of drill rod
The letter in W1, O1 and A2 tells you how that steel is hardened: in water, oil or air.
| Grade | Hardens in | What it's good at | Typical uses |
|---|---|---|---|
| W1 | Water | Most machinable; plain high-carbon steel (about 0.95 to 1.10% carbon) | Hammers, files, reamers; general shop work |
| O1 | Oil | The most widely used grade; good wear resistance and toughness | Dies, punches, gauges |
| A2 | Air | More wear resistance, safer hardening, less distortion than O1 | Parts that must keep their size after heat treatment |
| S7 | Air | The toughest and strongest; best for impact | Tools that take hard blows |
| D2 | Air | Highest wear resistance | Dies for long production runs |
| M2 | — | The most widely used high-speed steel | General high-speed tool work |
Sources: Windsor Steel for the grades, chemistry and ratings; McMaster-Carr for the W1 and O1 uses. McMaster lists O1 under ASTM A681 and W1 under ASTM A686.
Hardness: as sold and after heat treatment
Drill rod comes annealed, which means soft. McMaster's O1 rod is about Rockwell B90 and its W1 rod about Rockwell B95 as sold. Both can reach up to Rockwell C65 after heat treatment.
That's why drill rod is popular. You machine it while it's soft, then harden the finished part.
Sizes and tolerances
Windsor Steel lists these tolerances for round drill rod:
| Diameter | Diameter tolerance | Straightness (max) | Length tolerance |
|---|---|---|---|
| 0.124 in and smaller | ±0.0003 in | 0.005 in | +1/8 in, −0 |
| 0.125 to 0.499 in | ±0.0005 in | 0.005 in | +1/8 in, −0 |
| 0.500 to 3.000 in | ±0.0010 in | 0.005 in | +1/8 in, −0 |
Sizes come in fractions, decimals, number and letter drill sizes, and metric. McMaster-Carr sells O1 rod in lengths from 6 inches to 12 feet, with 36 inches among them.
Need to turn a fraction into a decimal? Use our fraction to decimal converter. The drill bit size chart lists number and letter sizes.
Uses
- Punches and drifts. Center punches, pin punches and alignment drifts.
- Pins and shafts. Dowel pins, guide pins and small shafts that need an exact round size.
- Dies and gauges. O1 is the usual pick for these, per McMaster-Carr.
- Small tools. McMaster-Carr lists hammers, files and reamers for W1.
- Shop-made jig parts. Guide pins and sleeves for a jig. Store-bought drill bushings are often other steels; Carr Lane makes its standard ones from 1144.
Drill rod vs similar stock
| Stock | What it is | Choose it when |
|---|---|---|
| Drill rod | Tool steel, ground round to a tight size, sold annealed | You need an exact size and a part you can harden |
| Tool steel flat or rough bar | The same grades in other shapes | The part isn't round, or you'll machine all faces |
| Ground and polished shafting | Precision round bar in other steels | You need a shaft, not a hardened tool |
| Plain round bar | Ordinary steel, not ground to tight size | Size and hardness don't matter much |
Hardening O1 drill rod: the basics
Starrett's directions for its O1 ground stock:
- Heat the part evenly to 1450 to 1500°F.
- Quench it in oil at 120 to 140°F. Never use water on O1.
- Temper it, holding it at the tempering heat for one hour for best toughness.
Metal Supermarkets adds a soak time of 30 minutes per inch of thickness at the hardening heat, and a normal tempering range of 300 to 450°F. It says to temper right after the quench.
W1 hardens in water instead, and A2 in still air. Each grade has its own heat-treat chart, so follow the supplier's sheet for the grade you buy.
How to choose drill rod
- Pick the grade. O1 for most tools. W1 if you want the easiest machining and can quench in water. A2 when size must not change much. S7 for tools that get hit hard.
- Pick the size. Order the finished size if you won't turn it down. Order a little bigger if you will.
- Plan the hardening. If you can't heat-treat, a hardening shop can.
- Plan the drilling. Drill and tap while the rod is still soft. Fully hardened rod is very hard to drill; see the best drill bit for hardened steel. Our types of drill bits guide compares the options.
- Tapping it? Look up the tap drill in our tap drill chart, and tap before you harden.
Drilling large holes in thick steel to mount your parts? A magnetic drill may be the tool for it.
Key takeaways
- Drill rod is tool steel in a precision-ground round bar. It isn't a drill bit, and it isn't the drill rods used to bore into rock.
- It comes annealed, so it machines easily. After heat treatment, W1 and O1 rod can reach up to Rockwell C65, per McMaster-Carr.
- Pick the grade by job: W1 is the most machinable, O1 is the most common, A2 moves less in heat treatment, and S7 is the toughest.
- Typical tolerance is ±0.0003 inch on rod 0.124 inch and under, ±0.0005 inch up to 0.499, and ±0.0010 inch from 0.500 to 3 inches.
- Drill rod vs tool steel: drill rod is tool steel. The name means the shape and finish, a ground round bar held to size.
Questions people ask
Is drill rod the same as tool steel?
Drill rod is tool steel. The name describes the form: a round bar, precision ground and held to a tight size. You can buy the same grades, like O1 or A2, as flat stock or rough bar too.
What is drill rod used for?
Parts that need an exact round size and a hard, wear-resistant finish: punches, pins, dies, gauges, reamers, small cutting tools and shafts. McMaster-Carr lists O1 for dies, punches and gauges, and W1 for hammers, files and reamers.
What is drill rod made of?
High-carbon or alloy tool steel. W1 is plain high-carbon steel, about 1% carbon. O1 adds manganese, chromium and a little vanadium. A2 has about 5% chromium plus molybdenum. Windsor Steel publishes the chemistry for each.
Is drill rod hard?
Not as you buy it. It comes annealed so you can cut, drill and turn it. McMaster-Carr's W1 rod is about Rockwell B95 as sold. After hardening and tempering, it can reach up to Rockwell C65.
What sizes does drill rod come in?
Fraction, decimal, number and letter sizes, plus metric. Lengths of 36 inches are common, and suppliers like McMaster-Carr also cut shorter and longer bars. Use a decimal chart to match a size to a bit or hole.
Can I harden drill rod at home?
Yes, if you can heat the part evenly to the right temperature and quench it the right way. Starrett says to heat O1 to 1450 to 1500°F and quench in oil, never water. Metal Supermarkets says to temper it right after the quench.
Sources
- Precision drill rod: grades W1, O1, A2, S7, D2, M2, chemistry, uses, diameter, straightness and length tolerances (Windsor Steel)
- Tight-tolerance oil-hardening O1 tool steel rods (drill rod): ASTM A681, annealed Rockwell B90, max Rockwell C65, lengths (McMaster-Carr)
- Tight-tolerance easy-to-machine W1 tool steel rods (drill rod): ASTM A686, annealed Rockwell B95, max Rockwell C65 (McMaster-Carr)
- 496 AISI O-1 precision ground stock: harden at 1450 to 1500°F, quench in 120 to 140°F oil, never water (Starrett)
- Tool steel O1: preheat 1200°F, harden 1475 to 1500°F, soak 30 min per inch, oil quench, temper 300 to 450°F (Metal Supermarkets)
- Understanding standard drill bushing types: 1144 steel, Rockwell C 62 to 64 (Carr Lane Manufacturing)
- Exploration underground: coring rods with SuperQ, RQ and other threads (Boart Longyear)
Change log: Nov 6, 2026: Merged two 2023 archive posts into one guide. Removed the mix-up with mining drill rods, the claim that drill rod goes in a drill chuck, and a fake shop pitch; added grades, tolerances, hardness and heat-treat facts from suppliers.
