Wood Drill Bits: Brad Point, Spade, Forstner and Auger

Choose the wood drill bit by the hole you want. A brad point bit makes clean round holes up to about 1/2 in (13 mm), a spade bit makes fast rough holes from 1/4 to 1-1/2 in (6 to 38 mm), a Forstner bit makes flat-bottom and overlapping holes, and an auger bit bores deep holes through framing and beams. A plain twist bit is fine for pilot holes. All of them run slower as the diameter grows.

Wood drill bit types at a glance

Bit	Typical size range	Best for	Weak point
Brad point	1/8 to 1/2 in (3 to 13 mm)	Dowel holes, cabinet work, accurate holes in hardwood and plywood	Small sizes only
Twist (HSS)	1/16 to 1/2 in (1.5 to 13 mm)	Pilot holes, general holes	Can skate on the surface, rough exit
Spade (paddle)	1/4 to 1-1/2 in (6 to 38 mm)	Rough holes in studs, wire runs	Tears the exit side, wanders
Forstner	1/4 to 4 in (6 to 100 mm)	Flat-bottom holes, hinge cups, overlapping holes	Slow, needs a steady hand or a drill press
Auger	3/8 to 1-1/2 in (10 to 38 mm)	Deep holes in framing, posts and beams	Needs a strong drill

Makers differ on exact size ranges, so check the printed range on the pack.

Which bit makes the cleanest hole?

A brad point bit makes the cleanest hole of the common types because its center spike holds the position and its two outer spurs cut the wood fibers before the flutes remove the waste. The rim of the hole comes out sharp, and the hole lands where you marked it. Forstner bits leave an even cleaner rim and are the usual choice for hinge cup holes in cabinet doors. For sizes and sets, see brad point drill bits.

When to use a spade bit

A spade bit is the fast, cheap way to bore a rough hole in construction lumber. A 3/4 in (19 mm) spade bit through a stud for a cable run is the standard job. The flat blade has no flutes to clear the chips, so pull the bit out now and then. To limit tear-out on the exit side, back the piece with a scrap board, or stop when the point appears and finish the hole from the other face.

When to use a Forstner bit

A Forstner bit cuts a flat-bottom hole, which no other bit in the table can do. The rim scores the circle and the cutting edges across the body shave the bottom flat, so it drills partial-depth holes, hinge cups (a 35 mm hole is the usual size for cup hinges) and holes that overlap each other. It generates a lot of heat, so run it at a low speed and clear the chips often. A drill press holds it steadiest; see drill press vs hand drill.

When to use an auger bit

An auger bit has a screw-thread lead on the tip that pulls it into the wood, and deep flutes that carry the chips out. That makes it the bit for long holes through a 4x4 post or through joists, as long as the drill has the torque to turn it. Because the lead pulls the bit forward, hold the drill firmly and keep it square.

How to drill a clean hole in wood

1. Mark the center with a pencil or a small awl dent.
2. Choose the bit for the hole type from the table above.
3. Set the speed. Small bits turn faster, large bits slower; the drill speed calculator gives a figure by diameter and material.
4. Clamp the piece so it cannot move.
5. Support the exit side with a scrap board.
6. Drill at steady pressure, back the bit out now and then to clear chips, and ease off as the bit breaks through.

For pilot holes before screws, match the bit to the screw with the pilot hole calculator. A countersink is a separate bit, covered in countersink drill bit sets.

Common mistakes

• Running a large Forstner or spade bit at full speed. Heat darkens the wood and dulls the edges.
• Pushing hard instead of clearing chips. The bit clogs and burns.
• Drilling straight through with no backer board, which splinters the exit side.
• Using a spade bit where the hole must be accurate.

For holes larger than about 1-1/2 in (38 mm), a hole saw is usually quicker than any of these.