Drill Bit Types Explained: Choosing the Right Bit for Each Material

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Most drilling problems people blame on the drill are actually bit problems. A burnt tip, a wandering hole, a split board, a bit that skates across tile — all of these usually mean the wrong bit, not an underpowered tool.

Here’s what each common bit type is for, and the failure mode that tells you you’ve grabbed the wrong one.

Twist bits — the default, and their limits

The bits in every starter set. Good general-purpose choices for wood, plastic and softer metals.

The coating matters more than people assume. Plain high-speed steel (HSS) is fine for wood and occasional light metal. Black oxide adds corrosion resistance. Titanium-coated bits last longer in metal — but the coating is a surface layer, so sharpening one removes exactly the thing you paid for. Cobalt bits alloy the hardness through the whole bit, which is why they survive stainless steel and why they cost more.

Failure sign: tip turns blue. That’s the steel losing its temper from heat — too much speed, too little pressure, no lubricant. A blued bit is permanently softened.

Brad point — for wood, when the hole location matters

A sharp centre spur plus two cutting wings. The spur bites exactly where you place it, so the bit doesn’t wander, and the wings slice wood fibres cleanly instead of tearing them.

Use these for dowel holes, shelf pins, anything where the hole has to be where you marked it and the rim has to look clean. Don’t use them on metal — the fine spur will snap.

Spade vs Forstner — both make big holes, very differently

Spade bits are for running cable through studs — fast, cheap, and nobody sees the hole. Forstner bits are for work that shows: concealed hinge cups, clean through-holes in a tabletop, flat-bottomed recesses.

Back the workpiece with scrap when using a spade bit, or the exit side will blow out.

Masonry bits — and why they need percussion

A carbide tip brazed onto a steel shaft. The tip doesn’t cut so much as pulverise, which is why it needs a hammer drill’s percussion to work properly.

Failure sign: you’re pressing hard and producing dust slowly, and the hole is barely deepening. Either you’re in hammer-off mode, or you’ve hit rebar. Neither is solved by pushing harder — withdraw the bit periodically to clear dust, which otherwise packs in and blocks cutting.

Tile and glass — the one that punishes impatience

Spear-point carbide or diamond-grit bits. Both need the same treatment: slow speed, no hammer, steady water cooling, light pressure.

Glazed tile is the classic disaster. The glaze is harder than the body underneath, so the bit skates across the surface and scratches it. Start at a shallow angle to break the glaze, then bring the drill upright once the tip is seated. Masking tape over the spot helps the bit bite.

Step bits — for sheet metal

Cone-shaped with stepped diameters. One bit covers a range of hole sizes and — importantly — leaves a clean edge in thin material instead of the triangular mess a twist bit makes when it grabs and tears sheet steel.

Quick reference

The one habit that saves the most bits

Slow down in hard material. The instinct when a bit isn’t cutting is to speed up and push harder — which generates heat, and heat is what destroys bits. Harder material wants lower RPM and steady, moderate pressure. In metal, add cutting oil and let the bit do the work.