Drill Bit Guide: Types, Materials, and Matching Bits to Materials

Twist Bits: The Universal Starting Point

High-speed steel (HSS) twist bits are the standard general-purpose bit. They drill wood, plastic, soft metals, and thin sheet metal. The two-flute spiral design clears chips from the hole as the bit advances. Sizes from 1/16 to 1/2 inch cover most fastener pilot holes and through-holes.

Cobalt bits (HSS with 5-8 percent cobalt content) handle harder metals — stainless steel, hardened bolts, and cast iron — without losing their temper. They cost more but last significantly longer in hard materials where standard HSS dulls in a few holes.

Black oxide coating reduces friction and extends life in wood and soft metal. Titanium nitride (TiN, gold-colored) coating is harder and lasts longer but cannot be resharpened — once the coating wears through, the bit performs like uncoated HSS. For bits you plan to resharpen, uncoated or black oxide is better.

Split-point tips start drilling immediately without walking (skidding across the surface). Standard 118-degree tips need a center punch mark to prevent walking on metal. For metal work, split-point bits save time and improve hole placement accuracy.

Wood-Specific Bits

Spade bits (paddle bits) cut flat-bottomed holes from 3/8 to 1-1/2 inches in wood. They are cheap, fast, and aggressive — good for rough holes in framing for wire and pipe. The hole quality is rough with tear-out around the edges. Not suitable for visible surfaces.

Forstner bits cut clean, flat-bottomed holes with smooth walls. They handle overlapping holes, angled drilling, and holes near board edges without deflecting. Essential for furniture work: hinge cups, dowel holes, and decorative recesses. Slower than spade bits and require a drill press for best results.

Brad-point bits are twist bits with a center spur that locates precisely and prevents walking. The outer spurs score the hole perimeter before the cutting lips engage, producing clean holes with minimal tear-out. The standard bit for visible holes in woodworking.

Auger bits have a threaded lead screw that pulls the bit into the wood, deep spiral flutes that clear chips from deep holes, and cutting spurs for clean entry. Use these for deep holes in timber framing and log building. The self-feeding action means the bit drills at its own pace — do not force it.

Masonry, Tile, and Glass Bits

Masonry bits have a carbide tip brazed to a standard steel body. They drill concrete, brick, block, and stone using a hammer drill's percussive action. The carbide tip crushes the masonry material rather than cutting it. Do not use them in rotary-only mode on hard concrete — the bit overheats and the tip breaks off.

SDS-plus bits fit rotary hammer drills (not standard chucks) and handle concrete drilling far more efficiently than masonry bits in a standard hammer drill. The SDS shank transmits hammer energy directly to the bit without slipping. For more than a few holes in concrete, rent a rotary hammer instead of struggling with a standard drill.

Glass and tile bits have a spear-shaped carbide tip that scratches and grinds through hard, brittle materials without cracking them. Start without hammer action, at low speed, with constant water cooling. Once through the hard surface layer, switch to a standard bit for the substrate behind.

Diamond-core bits are hollow cylinders with diamond-impregnated edges. They cut clean holes in porcelain tile, stone, and glass. They require water cooling during use and are sized to the exact hole diameter needed — no pilot bit, no step drilling.

Hole Saws and Step Bits

Hole saws cut large-diameter holes (3/4 to 6 inches) in wood, plastic, thin metal, and drywall. A center pilot bit locates the saw, and the toothed cylinder cuts the perimeter. The resulting plug pops out. Bi-metal saws (HSS teeth on a flexible body) handle both wood and metal.

Step bits (unibit) have a conical shape with multiple stepped diameters on a single bit. They drill progressively larger holes in thin material — sheet metal, electrical boxes, and panels — by driving deeper into the cone. One bit replaces a dozen twist bits for thin-material work.

Self-feed bits are large-diameter wood bits (1 to 4-5/8 inches) with a center screw and aggressive cutting teeth. They pull themselves through lumber quickly for rough holes in framing — plumbing, HVAC, and electrical runs. The self-feeding action demands a powerful drill with a side handle for control.

Adjustable hole cutters let you set a specific diameter using a sliding cutter arm. One tool covers a range of sizes, eliminating the need for dozens of fixed-size hole saws. Accuracy depends on setup precision — they produce rougher holes than dedicated hole saws.

Frequently Asked Questions