Open any drill bit set and you’re staring at a confusing pile of metal: twist bits, spade bits, brad points, hole saws, masonry bits. They all drill holes, but using the wrong one gives you splintered wood, burned bits, or a hole in the wrong place. Here’s what each type actually does.
Twist Bits: The Everyday Workhorse
The classic spiral bit in every set. Twist bits drill clean holes in wood, plastic, and thin metal. They’re the bit you’ll reach for 70% of the time.
Best for: Pilot holes, general-purpose drilling in wood and soft metal.
Tip: For metal, start slow with cutting oil. High speed on metal just overheats the bit and kills it.
Brad Point Bits: For Clean Wood Holes
Brad points have a sharp center spur that bites into wood before the cutting edges engage. That spur is the whole point — it stops the bit from wandering and leaves a clean entry hole with no tear-out.
Best for: Doweling, shelf-pin holes, any visible hole in finished woodwork.
Tip: If you’re drilling holes people will see, use brad points. The difference in cleanliness is night and day.
Spade Bits: Fast, Rough Holes in Wood
The flat paddle-shaped bits. They hog out holes fast and they’re cheap — but the holes are rough. Fine for running wires through studs; terrible for anything visible.
Best for: Rough carpentry, drilling through wall studs for wiring or plumbing.
Tip: Spade bits grab aggressively. Clamp your work and keep a firm grip, especially above 3/4 inch.
Hole Saws: For Big Diameter Holes
When you need a 2-inch hole for a doorknob or a 4-inch hole for a dryer vent, a hole saw is the answer. It’s a cup-shaped saw that cuts a circle.
Best for: Doorknob holes, recessed lights, vents.
Tip: Drill halfway from one side, then finish from the other. You’ll get a cleaner hole and the plug won’t tear out the back.
Masonry Bits: For Concrete and Brick
Masonry bits have a carbide tip brazed onto the end. They don’t cut concrete so much as pulverize it — which is why you use them with a hammer drill’s pounding action.
Best for: Concrete, brick, block, stone.
Tip: A regular drill on masonry just polishes the hole and burns the bit. If you’re drilling more than a couple of holes in concrete, borrow or rent a hammer drill.
The Material Cheat Sheet
- Softwood: Brad point or twist bit, medium speed
- Hardwood: Brad point, slower speed, back the bit out to clear chips
- Metal: Twist bit (cobalt for hard steel), slow speed, cutting oil
- Masonry: Masonry bit + hammer drill, no oil, steady pressure
- Tile/ceramic: Diamond or carbide-tipped glass/tile bit, very slow, water to cool
Speed and Pressure: The Two Things Beginners Get Wrong
The rule is simple: the harder the material, the slower the speed and the firmer the pressure. Beginners do the opposite — they run the drill at max RPM on everything and wonder why bits smoke and die. Let the bit cut; your job is just to guide it and clear the chips.
When to Replace a Bit
A sharp bit pulls itself into the work and throws clean chips. A dull bit needs you to push hard, squeals, and burns the wood. Sharpen twist bits with a bit sharpener or replace them — they’re cheap. Dull bits are how injuries happen.
Bit Coatings Compared: What the Colours Actually Buy You
Two bits with the same shape can differ in price by three times, and most of that difference is the coating. Here is what each one genuinely does:
| Coating / material | Colour | What it adds | Worth it for |
|---|---|---|---|
| Plain high-speed steel (HSS) | Bright silver | Baseline performance in wood and mild steel | Occasional drilling, wood only |
| Black oxide | Black | Light corrosion resistance, less friction in metal | General metal work on a budget |
| Titanium nitride (TiN) | Gold | Harder surface, longer edge life in metal — but only until the coating wears at the tip; sharpening removes it | Frequent drilling in steel and aluminium |
| Cobalt (M35/M42 alloy) | Dull bronze, through-hardened | Heat resistance through the whole bit, not a coating; survives stainless and cast iron, and can be resharpened | Stainless steel, hardened metals, regular trade use |
The honest summary: coatings help in metal and do almost nothing in wood, where sharpness and chip clearance matter more. For a woodworking-only shop, plain sharp HSS beats dull titanium every time.
Sharpen or Replace? A Simple Rule
A bit is worth sharpening if it is cobalt, a large diameter (over ½ inch), or part of a good set you want to keep complete. Small jobber bits under ¼ inch cost less than the time it takes to sharpen them well, and a badly hand-sharpened bit drills oversized, wandering holes. Whichever route you take, retire any bit that has turned blue or straw-coloured at the tip from overheating — the steel has lost its temper there, and no sharpening restores the hardness behind the discoloured metal.
Why do my drill bits keep snapping in metal?
Usually too much speed and too little feed pressure at the start, or the bit grabbing as it breaks through. Slow the drill down, keep steady pressure, and ease off the instant before breakthrough — most small bits die in the last millimetre of the hole.
Can I use wood bits in metal in a pinch?
Brad-point and spade bits, no — their points and spurs are shaped for fibres and will skate, overheat, and ruin themselves on steel. A standard twist bit is the only wood-shop bit that crosses over safely.
The Specialist Bits: Glass, Tile, and Masonry
Three materials defeat ordinary twist bits completely. Glass and glazed tile need a spear-point carbide bit or a diamond-grit hole saw, run slow, with the surface kept wet — water cools the cut and stops the glaze cracking from heat; even then, drill on the lowest speed your drill offers and let the grit do the work. Masonry needs a carbide-tipped bit in a hammer drill, where the hammering does as much work as the rotation; the same bit in a plain drill just polishes the hole and overheats. None of these specialists belongs in a general bit index — buy them per job, because their sizes follow the fixings you actually use.