Drill Bit Types, Materials & Sizes: The Complete Guide

Different Types of Drill Bits and What Each One Does

Every drill bit is engineered around a specific cutting geometry, and that geometry — not the brand or price tag — is what determines where it performs well.

The auger-versus-spade decision comes up constantly on wood jobs: choose an auger bit when hole accuracy and clean walls matter, and a spade bit when speed matters more than finish quality, such as rough electrical or plumbing runs that will be hidden anyway.

Drill Bit Materials Explained

Material determines hardness, heat resistance, and how long an edge holds before it needs sharpening or replacing.

• High-Speed Steel (HSS): The baseline material — affordable, holds an edge reasonably well in wood, plastic, and soft metals. Loses hardness above roughly 600°C.
• Cobalt (M35/M42): HSS alloyed with 5–8% cobalt. Retains hardness at higher temperatures, making it the standard for stainless steel and hardened alloys.
• Carbide-Tipped: A tungsten carbide insert brazed onto a steel body. Extremely hard and heat-resistant, but more brittle — it cuts masonry and abrasive materials that would dull steel almost instantly.
• Solid Carbide: The entire bit is carbide rather than just the tip. Used in CNC and production settings where rigidity and wear resistance justify the higher cost.
• Black Oxide / Titanium Coated: A surface treatment over HSS, not a different base material. The coating reduces friction and adds modest corrosion resistance but wears off with use.

Carbide vs HSS: Which One Actually Wins

This comparison gets asked more than any other, and the honest answer is that neither wins outright — the material has to match the workpiece.

A rule that holds up in practice: if the material can be cut with a hacksaw, HSS is usually sufficient; if it requires a masonry chisel or angle grinder, carbide is the right call.

Drill Bit Sizes Chart

Drill bits are sold under four overlapping sizing systems, and mixing them up is one of the most common ordering mistakes.

For tap drilling specifically, size selection isn't a guess — it follows published tap drill charts matched to thread pitch, since an undersized hole can snap a tap and an oversized one produces weak threads.

How to Choose the Right Drill Bit

Four questions narrow the decision every time, in this order:

1. What's the material? Wood, metal, masonry, tile, and plastic each rule out most of the catalog immediately.
2. What finish does the hole need? A flat-bottomed Forstner hole for hardware versus a rough pilot hole for a screw are different jobs even in the same board.
3. What's the depth and diameter? Deep holes favor augers or extended bits with good chip clearance; wide holes over roughly 25mm often need a hole saw instead of a twist bit.
4. What drill is driving it? A rotary-only drill can't effectively power a masonry bit — that needs hammer or SDS action to be efficient.

Best Drill Bits for Wood, Metal, and Concrete

How to Sharpen Drill Bits

A dull bit walks off-center, burns the material, and takes far more force to feed — all signs it's time to restore the edge rather than replace it.

1. Clamp the bit in a sharpening jig or drill doctor at the manufacturer's specified point angle — typically 118° for general-purpose bits, 135° for harder metals.
2. Grind one cutting lip at a time against a bench grinder or diamond wheel, keeping the angle consistent and removing minimal material per pass.
3. Check that both cutting edges are equal length; an uneven bit will drill oversized or off-axis holes.
4. Re-establish the relief angle behind the cutting edge so the bit can bite into material rather than just rub against it.
5. Test on scrap material before returning the bit to production use.

Carbide-tipped and solid carbide bits are the exception: they need a diamond grinding wheel, and for most shops it's more cost-effective to replace a chipped carbide bit than to resharpen it.

Drill Bit Maintenance Tips

• Clear chips regularly during deep holes instead of pushing through — packed chips generate heat that softens the cutting edge.
• Use cutting fluid or wax on metal to reduce friction and extend edge life between sharpenings.
• Store bits in a sized case or index rather than loose in a drawer, where edges chip against each other.
• Run the correct RPM for the bit diameter and material — too fast burns the edge, too slow increases wear from excess pressure.
• Wipe bits dry after use on metal to prevent surface rust from forming on the flutes.

Common Drill Bit Mistakes to Avoid

• Using a wood bit on metal or masonry, which dulls the edge in seconds and can snap the bit under load.
• Skipping a pilot hole before a larger bit, causing the tip to wander on hard or angled surfaces.
• Applying excessive downward pressure instead of letting the bit's geometry do the cutting — this is what causes overheating and premature dulling.
• Ignoring RPM settings; masonry and hole saws generally need lower speeds than small-diameter twist bits.
• Drilling without clearing chips on deep holes, which packs the flutes and can seize the bit mid-hole.

Drill Bit Buying Guide

For a shop or job site building out a working set, prioritizing in this order avoids the most common overspend-on-the-wrong-thing mistake:

1. A full HSS twist bit set covering common fractional or metric sizes for general wood, plastic, and light metal work.
2. A handful of cobalt bits in the most-used sizes for steel and stainless work.
3. A masonry set for concrete and brick, matched to the drill's chuck type — standard round shank versus SDS.
4. Task-specific bits added as jobs require them: Forstner for cabinetry, step bits for sheet metal, bellhanger or flex bits for cable and conduit runs.

Buying a large generic set upfront is usually less cost-effective than building a smaller, material-matched collection and adding specialty bits as specific jobs demand them.