Choosing the Right Drill Bit | Metal, Wood, Masonry & More

The right drill bit comes down to three things: the material you are drilling into, the diameter you need, and the type of hole required. For wood, use HSS twist or brad-point bits. For mild steel, use HSS. For stainless steel, use cobalt. For concrete and masonry, use carbide-tipped or SDS bits. For ceramic and porcelain tile, use diamond-tipped bits with no hammer action. Using the wrong bit — even by one category — risks damaging the bit, the material, or both.

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Drill Bit Materials Explained

High-Speed Steel (HSS)
High-speed steel is the standard material for general-purpose drill bits. It is harder than regular steel and retains its cutting edge at the temperatures generated by drilling wood, plastics, and mild steel. HSS bits are the correct choice for softwood, hardwood, MDF, plastics, aluminium, brass, copper, and mild steel. They are widely available, economical, and can be resharpened when they dull.

Cobalt (HSS-Co)
Cobalt drill bits are made from high-speed steel with 5–8% cobalt alloyed throughout the entire bit — not applied as a surface coating. The cobalt raises the heat resistance of the steel significantly, allowing the bit to maintain its cutting edge at higher temperatures. Cobalt bits are the correct choice for stainless steel, hardened steel, cast iron, and other hard or heat-generating metals. Because the cobalt runs through the full cross-section of the bit, cobalt bits can be resharpened repeatedly without losing their advantage. A cobalt bit will outlast a titanium-coated HSS bit by a significant margin on hard metals. For full coverage of cobalt drill bit grades (M35 vs M42 vs HSS-PM), stainless steel work-hardening, technique, brand selection and when cobalt beats HSS or needs carbide, see our Cobalt Drill Bit Guide.

Carbide-Tipped
Carbide-tipped bits have a tungsten carbide insert brazed onto a steel body. Carbide is extremely hard but brittle — it cannot flex and will crack if used on wood or metal. Carbide-tipped bits are designed exclusively for masonry: brick, block, concrete, render, and stone. They require hammer drill action to fracture the material rather than cut it. Standard carbide-tipped masonry bits are used in conventional hammer drills. For larger holes or denser concrete, SDS-Plus and SDS-Max bits use the same carbide tip geometry but are designed for rotary hammers.

Diamond-Tipped
Diamond-tipped bits use industrial diamond particles bonded to the cutting surface. Diamond is the hardest known material and can cut ceramic, porcelain, glass, and stone without fracturing them — provided no hammer action is used. Diamond bits require water cooling throughout the cut to prevent the diamond bond from overheating and failing. They are the only correct choice for porcelain tile; carbide-tipped alternatives are not hard enough for porcelain.

Coatings: TiN, TiAlN, Black Oxide
Coatings are surface treatments applied to HSS bits to improve hardness, reduce friction, or resist corrosion. Unlike cobalt, coatings do not penetrate the full material — once they wear through, the underlying HSS is exposed. Titanium Nitride (TiN, gold colour) is the most common coating and improves surface hardness and lubricity on mild steel and wood. Titanium Aluminium Nitride (TiAlN, dark purple-grey) offers better heat resistance and suits high-speed production drilling. Black oxide provides minor corrosion resistance with minimal performance improvement. Coated bits cannot be resharpened usefully, as resharpening removes the coating.

Drill Bit Types by Application

For Wood

HSS Twist Drill
The standard general-purpose drill bit. An HSS twist drill is the correct choice for softwood, hardwood, plywood, MDF, and particleboard when hole finish is not critical. The 118° included angle on a standard twist drill tends to tear wood fibres slightly at entry and exit; for cleaner holes in timber, use a brad-point.

Brad-Point Bit (Lip-and-Spur)
A brad-point bit has a sharp central spur that locates precisely on a mark and prevents the bit from wandering at entry. The two outer cutting spurs sever wood fibres cleanly before the flutes remove the waste, producing a significantly cleaner entry hole than a twist drill. Brad-point bits are the correct choice for precision joinery, dowel holes, furniture, and any application where hole quality matters. They are designed for wood only — do not use in metal.

Forstner Bit
A Forstner bit cuts a flat-bottomed cylindrical hole in timber. Unlike a twist drill or brad-point, it cuts from the outside diameter inward, which means it can be used to drill overlapping holes, angled holes, and holes near the edge of a workpiece without wandering. Forstner bits are the correct choice for hinge recesses, shelf-pin holes, and dowel jigs where a flat bottom is required. They perform best in a drill press; freehand use at large diameters is difficult to control.

Spade (Paddle) Bit
A spade bit has a flat paddle-shaped body with a central lead point. It removes material quickly and is suited to rough boring of large holes (16–50mm) in framing timber, structural work, and cable runs where finish is not critical. The flat body tends to tear exit surfaces; back the workpiece or reduce pressure before breakthrough.

Auger Bit
An auger bit has a threaded lead screw that pulls the bit into the timber without requiring drill pressure. This self-feeding action makes auger bits highly effective for deep holes in thick solid timber, particularly in hardwood, post, and beam work. The continuous helical flute evacuates chips efficiently from deep holes. Auger bits are typically used at low speed; the self-feeding screw requires torque control or the drill can wrench out of the operator's hands.

Hole Saw
A hole saw is a cylindrical saw blade mounted on an arbor with a pilot drill. It cuts large-diameter holes (typically 25–150mm+) in timber, sheet goods, and thin metal without removing the full core — the core is extracted after the cut. Hole saws are used for door lock sets, pipe penetrations, and cable entry points. Withdraw the saw regularly to clear chips and prevent binding.

For Metal

HSS Twist Drill
The standard choice for mild steel, aluminium, brass, copper, and most general metals. For best results in metal, use a 135° split-point geometry rather than the standard 118° — the split point self-centres without a pilot hole and reduces the axial force required to start cutting. Use cutting fluid on steel and reduce speed progressively as diameter increases.

Cobalt Twist Drill
Cobalt bits are essential for stainless steel. Stainless steel work-hardens under friction — if the bit slows, skids, or dwells without cutting, the surface hardens to a point where no HSS bit will penetrate it. The cobalt alloy provides the heat resistance to keep cutting under the sustained pressure required. Use slow speed, firm consistent feed, and cutting fluid from start to finish. Do not let the bit dwell.

Step Drill
A step drill is a conical bit with machined steps at increasing diameters, allowing a single bit to drill multiple hole sizes in sheet metal and thin plate. Step drills are the correct choice for electricians, auto electrical work, and general sheet metal work where multiple sizes are needed and material thickness is less than the step increment. They produce clean, burr-free holes in thin material without requiring a pilot hole.

Countersink Bit
A countersink bit creates a conical recess at the mouth of a drilled hole, allowing a flat-head or countersunk screw to sit flush with or below the surface. Used after drilling the clearance hole — not instead of it.

For Masonry and Concrete

Carbide-Tipped Masonry Bit
The standard choice for brick, block, render, and light concrete using a conventional hammer drill. The tungsten carbide tip fractures the material under impact rather than cutting it. Always use hammer mode — rotary-only mode in masonry generates heat without progress and will destroy the bit. Not suitable for reinforced concrete where rebar stops the bit.

SDS-Plus Bit
SDS-Plus bits have a slotted shank that locks into an SDS-Plus rotary hammer chuck, allowing the bit to slide axially under the hammer mechanism while remaining rotationally locked. This produces significantly more impact energy than a conventional hammer drill and is the correct choice for concrete drilling above 6mm diameter. SDS-Plus is the standard domestic and light commercial format, covering holes up to approximately 26mm in concrete.

SDS-Max Bit
SDS-Max uses a larger shank format designed for heavy-duty rotary hammers. It is used for large-diameter holes in dense or reinforced concrete and demolition work. SDS-Plus and SDS-Max are not interchangeable — the shanks are different sizes.

Diamond Core Bit
A diamond core drill removes a cylindrical plug from concrete, stone, or reinforced masonry using continuous water cooling. It is used for large-diameter holes (typically 50mm+) in structural concrete where a rotary hammer cannot produce the required diameter, or where no hammer action can be used. Requires a dedicated core drill rig or stand.

For Tiles and Glass

Diamond-Tipped Tile Bit
Diamond tile bits cut ceramic, porcelain, and glass by grinding rather than cutting. They must be used with no hammer action — hammer mode will crack and shatter the tile. Water cooling is required throughout the cut; without it, the diamond bond overheats and the diamonds release from the matrix. For porcelain specifically: carbide-tipped spear-point bits will cut ceramic tile but will fail within a hole or two on porcelain. Use diamond for both without exception.

How to drill tile without cracking it:

1. Mark the hole and apply masking tape over the glaze to prevent the bit skating on the glazed surface
2. Fit a diamond-tipped tile bit and confirm the drill is in rotary-only mode — no hammer action
3. Create a small water reservoir around the hole using a ring of plumber's putty
4. Start at very low speed with light pressure until the bit establishes a groove
5. Increase speed slightly once the bit has started cutting
6. Maintain water flow throughout — never let the bit run dry
7. Reduce pressure just before breakthrough to avoid cracking the back face of the tile

For Plastics

HSS twist drills work for most plastics, but the standard 118° geometry tends to grab at breakthrough and can crack brittle materials like acrylic and polycarbonate. For clean holes in acrylic, use a brad-point bit or a purpose-made plastic-cutting bit with modified geometry. Reduce speed, apply light consistent pressure, and back the workpiece against a solid surface to prevent flex at breakthrough. For polycarbonate — which is tougher and less brittle than acrylic — a standard sharp HSS bit at medium speed works well.

Shank Types Explained

The shank is the part of the bit that is clamped in the drill chuck. The wrong shank type will not fit, will not hold, or will damage the chuck.

Morse taper shanks are the standard for drill press and lathe tooling where precision concentricity matters. MT2, MT3, and MT4 are the most common drill press socket sizes in Australian workshops, but identifying an unmarked taper — or selecting the right adapter sleeve — requires knowing the exact bore dimensions. See our Morse taper guide for MT0–MT7 dimensions, drill press compatibility, adapter selection, and stuck taper removal.

Drill Bit Coatings: What They Actually Do

The critical distinction: cobalt is an alloy, not a surface treatment. The cobalt runs through the entire bit, so the heat-resistance property is present from the surface to the core. A TiN-coated HSS bit provides better performance than plain HSS on mild steel, but once the coating wears through — typically after resharpening — it reverts to plain HSS performance.

Getting the Speed Right

Running too fast generates heat, blunts the cutting edge, and work-hardens metal. Too slow and the bit pushes instead of cuts. Larger diameter and harder material both require lower speed.

Cutting fluid: Essential for steel and stainless — apply at start and maintain throughout. WD-40 works well for aluminium. Cast iron is drilled dry. Wood and masonry require no fluid.

Key warning sign: If the bit produces fine metallic powder or blue/straw discolouration on steel rather than chips, the speed is too high. Drop the speed and apply fluid.

How to Know When a Drill Bit Is Blunt

A sharp drill bit cuts; a blunt one pushes and scrapes. Signs a bit needs resharpening or replacement:

• Requires noticeably more pressure than the same bit did previously
• Produces dust or fine powder rather than chips (on metal or wood)
• The bit or workpiece gets hot quickly, even at correct speed with fluid
• The entry hole is rough, torn, or oversized on wood
• Squealing or chattering on metal — the cutting edge is skidding rather than cutting
• Visible edge damage under close inspection — chipping, rounding, or a flat on the cutting lip

HSS and cobalt bits can be resharpened on a bench grinder using a drill bit sharpening attachment or by hand if you know the geometry. Carbide-tipped masonry bits can be dressed with a diamond file. Coated bits should generally be replaced once blunt, as resharpening removes the coating.

Common Mistakes

Using HSS on stainless steel. Stainless work-hardens under friction. An HSS bit running too fast or without fluid will skid across a hardened surface within seconds. Use cobalt, slow speed, and cutting fluid from the first moment of contact.

Using a masonry bit on ceramic or porcelain tile. The hammer action fractures tile instantly. Diamond-tipped bit, no hammer mode, with water cooling throughout.

Using a masonry bit on wood or metal. A carbide-tipped masonry bit will drill through wood, but the geometry is wrong — it tears rather than cuts, and the hammer action will split timber. Use the correct bit type for the material.

Speed too high on metal. The most common cause of blunted metal-drilling bits. Slow down, add fluid, keep the bit moving without dwelling.

No centre punch on metal. Without a punch mark, the bit skates across the surface before biting in. A centre punch takes five seconds and prevents a wandering hole — and for accurate layout the two-stage prick-punch-then-centre-punch technique plus filing off the raised metal afterwards is the workshop standard.

Running a round-shank bit in an impact driver. Impact drivers are designed for hex-shank bits. Round-shank bits can slip, damage the chuck, and snap under the impact mechanism's rotational hammering.

Too much pressure near breakthrough. On wood and tile especially, the force needed to push through the final skin of material can crack the exit face. Reduce pressure just before the bit clears.

Using a dull bit and compensating with pressure. More pressure means more heat, faster wear, and a worse hole. The correct fix is to resharpen or replace.

Confusing a drill bit with an end mill. Drill bits cut on the tip and are designed to plunge straight down. End mills cut on both the end and the sides and are designed for sideways feed milling. They are not interchangeable — using a drill bit for sideways milling will deflect the bit and either break it or produce an oval hole. For end mill selection, types, flute count and coatings see our End Mill Guide.

Frequently Asked Questions

What is the best drill bit for stainless steel?
Cobalt drill bits (HSS-Co, 5–8% cobalt content) are the correct choice for stainless steel. Stainless work-hardens rapidly under friction — standard HSS bits cannot maintain their cutting edge and will fail within seconds on a work-hardened surface. Use slow speed, firm consistent pressure, and apply cutting fluid throughout. Do not let the bit dwell or skate without cutting.

Can I use a masonry bit on wood?
Technically a carbide-tipped masonry bit will pass through wood, but it is the wrong tool. The geometry is designed to fracture brittle material under impact, not to slice wood fibres. In wood, a masonry bit produces a rough, torn hole and the hammer action will split timber. Use an HSS twist drill or brad-point for wood.

What happens if I use the wrong drill bit?
The consequences depend on how wrong the mismatch is. Using a wood bit on mild steel will dull the bit quickly and produce a poor hole. Using an HSS bit on stainless will work-harden the stainless and leave the bit useless in under a minute. Using a masonry bit on tile with hammer action will crack and shatter the tile. In most cases the cost is a ruined bit; in some cases — tile and stainless in particular — the workpiece is also ruined.

What is the difference between SDS-Plus and SDS-Max?
SDS-Plus is the standard slotted-shank format for rotary hammer drills up to approximately 26mm capacity. SDS-Max uses a larger shank for heavy-duty rotary hammers used in large-diameter or deep drilling in concrete. The two formats are not interchangeable — SDS-Max bits will not fit an SDS-Plus chuck and vice versa. Always check which format your rotary hammer uses before purchasing bits.

How do I drill through ceramic or porcelain tile without cracking it?
Use a diamond-tipped tile bit with no hammer action whatsoever. Mark the hole, apply masking tape over the glaze to prevent skating, and create a small water reservoir with a ring of plumber's putty. Start at low speed with light pressure until the bit establishes a groove, then increase speed slightly. Maintain water cooling throughout and reduce pressure just before breakthrough. Porcelain is significantly harder than ceramic — carbide spear bits are not adequate for porcelain. Use diamond for both.

What is the best drill bit for hardwood?
A sharp brad-point bit is the best choice for hardwood when hole quality matters — the central spur locates precisely and the outer spurs sever fibres cleanly before the body removes the waste. For rough work or deep holes, a sharp HSS twist drill works well at medium speed. Ensure the bit is sharp — a dull bit in hardwood requires excessive pressure and burns both the bit and the timber.

Can I use drill bits in an impact driver?
Only hex-shank bits specifically rated for impact use. Standard round-shank drill bits are not designed for the rotational hammering of an impact driver and can slip, snap, or damage the chuck. Hex-shank HSS twist drills and hex-shank masonry bits work well in impact drivers for light drilling. For larger holes or harder materials, use a drill driver or hammer drill.

How do I know when a drill bit is blunt?
A blunt bit requires noticeably more pressure than before, produces dust or powder rather than chips, causes rapid heat build-up, and leaves a rough or oversized hole. On metal, a blunt bit may squeal or chatter rather than cut cleanly. HSS and cobalt bits can be resharpened on a bench grinder; coated bits (TiN, TiAlN) should be replaced as resharpening removes the coating.

What drill bit size do I need for a specific screw?
For a clearance hole (where the screw passes straight through without gripping), use a bit equal to or slightly larger than the screw's outer thread diameter. For a pilot hole in timber (where the screw threads in and grips), use a bit approximately equal to the screw's core diameter — roughly 60–70% of the outer diameter for most wood screws. For machine screws tapped into metal, the correct pilot drill depends on thread pitch and material. See our Drill Bit Size Chart: Metric, Imperial & Fractional.