The material is part of the design
Two bits that look the same can be made of very different steel and finished in very different ways. The material and coating decide how hot a bit can run before it dulls, how hard a surface it can cut and how likely it is to snap. Matching them to what you are drilling is often the difference between a bit that lasts years and one that is ruined in a single hole.
Carbon steel
Plain carbon steel bits are inexpensive and take a sharp edge. They are generally fine for softwood and some soft plastics. They lose their hardness when they get hot, so they dull quickly in metal. Treat them as wood bits and they are usually adequate for light work.
High-speed steel
High-speed steel, often shortened to HSS, is the standard material for general-purpose metal-cutting twist bits. It keeps its hardness at higher temperatures than carbon steel, so it handles mild steel, aluminum, brass and wood. For many home workshops, a set of HSS bits is the most versatile single purchase. Resharpening is possible with the right grinder or jig, and sharpening techniques are worth learning if you use these bits often.
HSS bits are usually sold with a surface finish, which is where the colors come from.
Common coatings
- Black oxide. A dark chemical finish that helps resist rust and reduces friction a little. It suits general work in wood and mild metals and is a modest upgrade over a bare bit.
- Titanium nitride (gold). A thin, hard, slippery layer that typically helps a bit run cooler and last longer. The coating is only on the surface, so once you sharpen away the gold the benefit is largely gone.
- Other hard coatings. Some bits carry additional coatings meant for tough metals. Their descriptions vary by maker, so read the packaging for what material the bit is designed for rather than assuming.
A coating does not turn a wood bit into a metal bit. Cutting geometry and the base steel still matter.
Cobalt alloy
Cobalt bits are made from steel alloyed with a few percent of cobalt, rather than coated with it, so the properties run all the way through. They tolerate heat better than standard HSS and are typically chosen for hard metals such as stainless steel and cast iron. The trade-off is that they are usually more brittle, so they can snap if you flex or force them. They are also generally more expensive than basic HSS.
For stainless steel and similar metals, slow speed, steady pressure and cutting lubricant matter at least as much as the bit. The techniques are covered in guidance on drilling metal.
Carbide
Carbide is a very hard material that holds an edge far longer than steel but is brittle. It appears in two forms:
- Carbide tips on masonry bits. The tip is brazed to a steel body and is what makes drilling brick, block and concrete possible.
- Solid or tipped carbide for metal, tile or abrasive materials. These cut hard or abrasive workpieces, but they dislike wobble and side loads, so they are typically used in a drill press or a rigid setup.
Carbide bits are mostly chosen when you need lifespan in abrasive material or have to cut something steel cannot.
Diamond
Diamond-coated or diamond-grit bits are made for glass, ceramic tile and similar hard, brittle material. They grind instead of cut and generally need water to stay cool. Follow the maker’s instructions closely, since speed and lubrication are critical.
Matching material to the job
| Material you are drilling | Typical bit material |
|---|---|
| Softwood and hardwood | Carbon steel or HSS, in a wood-style bit |
| Mild steel, aluminum, brass | HSS, sometimes with black oxide or titanium nitride |
| Stainless steel, hard alloys | Cobalt alloy, with slow speed and lubricant |
| Brick, block, concrete | Carbide-tipped masonry bit |
| Tile, glass | Diamond or specialty carbide-tipped bit |
This is a guide, not a rule. Wood species also vary: dense hardwood, for instance, can dull a bit faster than a soft one, and the wood grain affects how cleanly any bit enters and exits.
Making bits last
- Keep the speed appropriate: slower for larger bits and harder metals.
- Use cutting oil on steel, and clear chips often.
- Do not lean on a dull bit. If it squeals, smokes or needs a lot of force, stop and look at it.
- Store bits in an index or case so the edges do not knock together, and wear safety glasses when drilling.
- Wear safety glasses and clamp the work. Remove the battery or unplug the drill before changing bits.
Outcomes depend on the drill, the material and your technique, so treat these descriptions as typical rather than guaranteed.