What Drill Bit to Use for Wood: Every Type Explained in Plain English

For holes in wood up to about 10mm, a brad point bit is the right answer and an ordinary HSS twist bit will do at a push. Above that, the choice comes down to how tidy the hole needs to be: spade bits for rough and fast, augers for deep, Forstner bits for clean flat bottomed holes.

The quick answer by hole size

• Under 10mm, general purpose: brad point bit, or HSS twist bit if that is what you have.
• 10mm to 25mm, hole does not need to be pretty: spade bit.
• 10mm to 25mm, hole needs to look good: Forstner bit.
• Deep holes through joists and thick timber: auger bit.
• 25mm and above, through thin material: hole saw.
• Pilot holes for screws: small HSS twist bit, ideally with a countersink.

Twist bits: the ones already in your box

Standard HSS twist bits are made for metal, but they cut wood well enough and most people use nothing else for small holes. The drawback is the tip: a chisel point skates across the surface before it bites, so it wanders off your mark and leaves a ragged rim.

Mark the centre with an awl or nail punch so the tip has somewhere to sit, then start slowly. Buy HSS rather than carbon steel: carbon steel takes a keen edge but loses its temper as soon as it gets hot.

Brad point bits: the wood specialist

A brad point bit looks like a twist bit with a sharp spur in the middle and two raised cutting edges on the outside. That centre spur plants itself exactly where you put it, and the outer spurs slice the wood fibres before the main flutes lift them out. The result is a hole that starts on the mark and has crisp edges rather than fuzz.

If you do a reasonable amount of woodwork, a set of brad points from 3mm to 10mm is the most worthwhile upgrade you can make. They are far better in plywood and veneered board, where a twist bit will happily tear the top layer.

Spade bits: cheap, fast and rough

A spade bit, sometimes called a flat bit, is a flat blade with a long point in the middle. They are cheap, they remove wood fast, and they are what most people reach for when running cable or pipe through studs. The trade off is finish: the exit side blows out and the walls are never smooth.

Run them at reasonably high speed with steady pressure rather than leaning on the drill. When the centre point breaks through the far side, stop, flip the work over and finish from the other face, or clamp a sacrificial offcut behind it before you start.

Auger bits: for deep holes

Auger bits have a threaded lead screw that pulls the bit into the timber and a wide single flute that clears chips out of a deep hole. That chip clearing is the point: a spade bit packs a deep hole with dust and starts burning, while an auger keeps ejecting waste all the way through a 100mm beam.

Because the lead screw does the feeding, you barely push at all. Let it pull itself in and run it slowly. Short pattern augers suit cordless drills; the long carpenter's pattern is really for a corded drill or brace.

Forstner bits: clean holes with flat bottoms

Forstner bits cut with a rim rather than a point, so they produce flat bottomed holes, overlapping holes and holes right at the edge of a board without wandering. Anyone fitting concealed kitchen hinges knows the 35mm one. They generate heat, so run them slowly and back the bit out every few seconds to clear chips. A scorched Forstner hole usually means too much speed, not a blunt bit.

Hole saws for the big stuff

Past about 30mm, a hole saw is cheaper and lighter work than a huge Forstner because it cuts only the perimeter. Use the slowest speed available, keep it square, and pull out regularly to eject the waste plug. Carbide toothed versions are worth the extra in chipboard and MDF, which blunt plain steel fast because of the glue content.

Pilot holes and countersinks

Screws split wood because the solid core of the screw is trying to occupy space the timber will not give up. A pilot hole makes that space. Drill it to roughly the core diameter of the screw, which is the shank measured between the threads.

1. 3.5mm screw: about 2mm in softwood, 2.5mm in hardwood.
2. 4mm screw: about 2.5mm in softwood, 3mm in hardwood.
3. 5mm screw: about 3mm in softwood, 3.5mm in hardwood.

In hardwood, oak and beech especially, go up a size rather than down. A combination pilot and countersink bit does both jobs in one plunge and stops the screw head standing proud.

Speed matters as much as the bit

The rule is simple: small bits fast, big bits slow. A 3mm brad point is happy at full speed, a 35mm Forstner wants around 500rpm. Too fast shows up as burnt brown rings and a bit that stops cutting; too slow shows up as the drill bogging down and chattering. Let the bit cut and use pressure only to keep it engaged.