Drill Bit Types Explained: When to Use Each One

Twist Bits: The Default

Twist bits are the standard bits that come in every drill bit set. Two helical flutes spiral around a cylindrical body, cutting on the tip and clearing chips up the flutes. They work in wood, plastic, soft metal, and with HSS (high-speed steel) or cobalt versions, in harder metals. Sizes go from 1/16-inch to 1/2-inch in standard sets. Beyond 1/2-inch, you need a reduced-shank bit that steps down to a 3/8 or 1/2-inch shank to fit a standard chuck.

For wood, twist bits are fine for small holes up to about 3/8-inch. Larger holes in wood are better served by spade bits or Forstner bits because twist bits wander and the entry hole can splinter. For metal, HSS twist bits work on mild steel and aluminum. Cobalt bits (5% cobalt alloy) handle stainless steel and hardened fasteners.

Spade Bits: Fast and Rough

A flat blade with a center point, sized from 3/8-inch to 1-1/2-inch. Spade bits bore through wood fast. They throw big chips, leave a rough hole, and are cheap enough to be disposable. Electricians and plumbers use them to drill through studs and joists for wire and pipe runs. A 3/4-inch spade bit puts a Romex-sized hole through a 2x4 in about 2 seconds.

Don't use spade bits for visible work. The entry and exit holes splinter, and the hole walls are rough. For clean holes in cabinet sides, furniture, or finish trim, use a Forstner bit. Keep spade bits sharp by touching up the cutting edges with a flat file.

Forstner Bits: Clean and Flat

Forstner bits cut flat-bottomed, clean-edged holes from 1/4-inch to 2-1/8-inch. A center spur guides the bit while a rim cutter scores the wood fibers before the body removes the material. The result is a hole with no splintering and a flat bottom, which twist and spade bits can't produce. They're slower than spade bits and work best in a drill press at 500 to 1,000 RPM.

Standard uses: 35mm hinge cups for European cabinet hinges, counterbores for bolt heads, overlapping holes for mortises, and any decorative or structural hole in visible work. Forstner bits also cut overlapping holes without the center point drifting into the adjacent hole, which makes them essential for rectangular mortises.

Hole Saws: Big Circles

A cylindrical blade mounted on a mandrel with a pilot bit in the center. Hole saws cut circles from 3/4-inch to 6 inches in wood, plastic, drywall, and thin metal. The pilot bit keeps the saw centered while the teeth cut the perimeter. Bi-metal hole saws handle wood and metal. Carbide-grit saws handle tile and cement board.

Common uses: door locksets (2-1/8-inch), recessed lighting (various sizes), plumbing penetrations, and junction box openings. Run hole saws slowly (300 to 800 RPM) and back out frequently to clear chips. Forcing a hole saw overheats the teeth and work-hardens the material.

Masonry Bits: Concrete and Brick

Masonry bits have a carbide tip brazed onto a steel body. The tip is wider than the body so the flutes clear the hole without binding. They work with the hammer mode on a hammer drill, where the pulsing action pulverizes the masonry while the rotation clears debris. Sizes range from 3/16-inch (for tapcon screws) to 1/2-inch (for concrete anchors).

For holes larger than 1/2-inch or in reinforced concrete, switch to a rotary hammer with SDS-Plus bits. Standard masonry bits in a hammer drill top out at about 1/2-inch diameter before the tool can't deliver enough impact energy.

Step Bits: Sheet Metal and Thin Stock

A conical bit with stepped diameters increasing from tip to base, usually covering 1/8-inch to 7/8-inch or wider in one bit. Each step is labeled with its diameter. Step bits cut clean, round holes in sheet metal, electrical panels, ductwork, and thin plastic. They can't bore deep holes because the cone widens as it goes. Maximum material thickness is about 1/8-inch per step.

Step bits self-deburr as they cut, leaving a clean hole with no sharp edges. They're the fastest way to drill multiple sizes in sheet metal without changing bits. Keep them sharp with a diamond file on the step edges.

Frequently Asked Questions