Drill bit types: twist, brad-point, spade, Forstner, step, masonry and more

01What are the main types of drill bit?

Drill bits fall into six working groups by the material they are made to drill: general-purpose twist bits, wood bits, sheet-metal bits, masonry bits, tile and glass bits, and hole saws for holes larger than a bit can cut. Within each group, the point shape, the cutting material and the coating decide how well a given bit suits the job.

The names most people meet on a rack are twist (or jobber) bits, brad-point bits, spade (or paddle) bits, Forstner bits, auger bits, step (or unibit) drills, masonry and SDS bits, diamond core bits and spear-point glass bits. Some names describe the shape of the point, such as brad-point and split-point; others describe the material, such as cobalt or carbide; others describe the length, such as stub, jobber and long-series. A single bit can carry all three: a jobber-length, split-point cobalt twist drill is one specific bit.

The table below sums up which bit type each material calls for. The sections after it take each group in turn, with the point angles, materials, lengths and shanks that separate one bit from another. For buying advice by material, the drill bits by material hub links every guide on the site.

02What is a twist drill bit, and which point angle should it have?

A twist bit is the general-purpose drill bit: two helical flutes carry chips out of the hole while two cutting lips at the tip do the cutting. The common general-purpose version has a 118 degrees point, which works in wood, metal and plastic.

The point angle is the angle between the two cutting lips, and it is the figure people mean by drill bit angle. A flatter point bites into harder material; a sharper point suits soft material. The reference table below gives point angles of 118–135 degrees for mild and stainless steel and a much sharper range for plastics; these figures come from Wikipedia's tool-geometry table, which cites a machining reference, and no maker's chart was available to confirm them. Starrett notes that 135 degrees split-point HSS drills are self-centring, start more easily, need less feed pressure and wander less. A split point has the chisel edge at the very tip ground away, so the bit starts cutting at once instead of skating.

Twist bits are sold in four sizing systems: fractional inch, metric, number and letter. The drill size chart with decimal equivalents lists every size side by side, and the same sizes feed the metric tap drill sizes and the pilot hole sizes for screws charts.

03What is the difference between HSS, cobalt and carbide drill bits?

They are different cutting materials. High-speed steel is the standard: it drills metal, hardwood and most other materials, and has largely replaced plain carbon-steel bits. Reference sources such as Wikipedia describe cobalt HSS as holding its hardness at higher temperatures, which suits stainless steel and other hard materials, and tungsten carbide as harder again, holding an edge longest but much more brittle than steel.

A common mix-up is to treat cobalt as a coating. It is not: a cobalt bit is a high-speed steel alloy with cobalt in the steel itself, usually sold under two grades: M35 (also called HSS-E) is M2 high-speed steel with 5% cobalt added, and M42 is a molybdenum HSS with 8% cobalt. IRWIN's M-35 set shows how such a set is laid out: it runs 1/16 to 1/2 by 1/64 in steps with split points, per IRWIN's listing. Black oxide and titanium nitride (TiN), by contrast, are surface coatings on an ordinary HSS bit. The life gains claimed for coatings in our sources come from limited references or from makers; Milwaukee, for example, claims longer life for its RED HELIX titanium bits than for its black-oxide bits. Treat such figures as maker claims. Independent lab figures are scarce. One 2008 Tribology in Industry study, drilling a 12% chromium steel dry with 7 mm M2 HSS twist drills, counted 29 vs 3 holes before failure for a TiN-coated drill against an uncoated one, while in mild steel all three drills it tested lasted the full run. It is an older study and among the few open-access direct comparisons: a coating earns its keep in hard, hot cutting, and makes little difference in mild steel.

For metal work, the bits most worth choosing carefully are those for stainless and hardened steel, where a plain HSS bit dulls quickly. The guide to bits for stainless and hardened steel compares cobalt and other options by published spec.

04Which drill bits are made for wood?

Four bit types are made for wood, as reference sources including Wikipedia group them: brad-point bits for clean, accurate small holes, spade bits for fast rough holes, Forstner bits for clean flat-bottomed holes, and auger bits for deep holes. An ordinary HSS twist bit also drills wood, but it tends to wander and tear the exit side.

A brad-point (lip and spur) bit is a twist bit optimised for wood: a sharp centre spur holds it on the mark, and the outer spurs score the rim before the lips lift the waste. Spade bits are flat paddles with a centre point; they cut fast in a hand drill but splinter where they exit, and versions with spurs on the cutters leave a cleaner hole. Forstner bits bore precise, flat-bottomed holes in any grain direction and can overlap one hole with another or cut on the edge of a board, but they cannot clear their own chips and must be withdrawn often. Auger bits add a long spiral flute to clear chips from deep holes, and the common Jennings pattern has a self-feeding screw tip, two spurs and two cutting edges.

What sizes do auger bits come in?

Auger sizes from Milwaukee's accessory catalogue give a typical spread. Milwaukee lists ship auger bits from 3/8 to 1-1/2 in, in short and long versions with impact-rated shanks, and spur auger bits from 1/2 to 1-1/2 in. Whatever the diameter, the long spiral flute is what carries chips out of the hole. No maker speed chart for auger bits was available, so this page does not give auger speeds.

The difference that matters most in use is speed. Recommended speed falls as diameter rises, and large Forstner bits are run slowly to avoid scorching. The comparison of wood boring bits compared sets out hole quality, sizes and speed charts for these three bits side by side.

05What is a step drill bit used for?

A step drill, also sold as a unibit, is described in reference sources such as Wikipedia as drilling a range of hole sizes with one bit: its cone is cut into a series of steps, each a larger diameter than the one before. It is mainly used in sheet material such as thin steel, aluminium and plastic, where a large twist bit would grab and tear the sheet.

Because each step is short, a step bit only drills thin stock to its full size; on thicker material the hole stops at whatever step has reached through. The step bit picks page compares step ranges and steel grades.

06Which bits drill concrete, brick and stone?

Masonry bits drill concrete, brick and block. They have a brazed tungsten carbide tip and are normally used with hammer action, either in a hammer drill with a round or hex shank or in a rotary hammer with an SDS shank. Starrett's SDS-plus masonry bits use a 130 degrees carbide tip.

Hammer action has a cost in vibration. HSE's L140 guidance, in the 2019 second edition that is still current, gives 11 m/s² as its recommended starting estimate for an impact (hammer) drill with a 5 to 8 mm masonry bit, more than double its figure for a drill with a standard bit; the table is based on tools in use before 2015. HSE also notes that keeping bits sharp and not over-pushing lowers vibration, so a worn masonry bit is worth replacing rather than forcing.

SDS shanks are slotted so a rotary hammer can deliver its blow while the bit slides back and forth in the holder. The two common sizes are SDS-plus, with a 10 mm shank, and SDS-max, with an 18 mm shank, and the two are not interchangeable. Hilti labels its SDS-plus connection TE-C. The guide to SDS-plus and SDS-max shanks explains which hammers take which bits, and the picks for masonry drill bits cover sizes for anchors and plugs.

07Which bits drill tile, porcelain and glass?

Diamond core bits and diamond hole saws drill porcelain, stone and glass, and carbide spear-point bits drill glass. Both work by grinding rather than cutting, and both need low speed and cooling.

Starrett says diamond tile drills and diamond hole saws must always be cooled with water. Wikipedia describes glass bits as having a spear-shaped carbide point, run at low speed, that gets hot and wears quickly. The idea that tile and glass drill faster at high speed is wrong on both counts: speed adds heat, and heat is what destroys these bits and cracks the work. For tile-specific choices, the tile and porcelain drill bits page compares spear-point and diamond options.

Does a glass and tile bit drill porcelain?

Not according to the makers. Milwaukee says its carbide ceramic tile and glass bits are not recommended for porcelain tile, and Bosch points porcelain jobs to its HEX-9 HardCeramic bit. Diamond bits are the type sold for porcelain.

Should tile be drilled with hammer action?

No. Bosch says to drill ceramic tile on the rotary setting only, Milwaukee says its tile and glass bits are for drill drivers only, and Makita says its tile bits are for a driver-drill. Bosch adds that the hole should be started slowly with light pressure, raising pressure and speed once the bit has bitten. That is the opposite of a masonry bit, which relies on hammer action.

08When do you need a hole saw instead of a drill bit?

You need a hole saw when the hole is larger than a drill bit can practically cut, or when you only want to remove a ring of material. A hole saw is a toothed cup that mounts on an arbor carrying a pilot drill, and it cuts only the rim of the hole, leaving a solid core.

Hole saws come in the same material families as bits. Bi-metal saws cut metal, including stainless sheet, as well as wood and plastic; carbide-tipped saws are for non-metallics such as wood, MDF, plasterboard and tile; and diamond-grit saws cut glass, ceramics, porcelain and stone with water cooling. Standard bi-metal saws cut about 1-5/8 in deep, so thicker work needs a deep-cut saw or a cut from both sides. The hole saw sizes for pipe and conduit chart lists sizes for common fittings, and hole saw kits are compared on a separate page.

09What are jobber, stub and long drill bit lengths?

Reference sources such as Wikipedia list three length series for twist drills: stub (also called screw-machine) length, which is short and stiff; jobber length, the medium length and the most common; and taper or long-series length for deep holes. Jobber length is what most retail drill sets contain.

Shorter bits flex less, so they start more accurately and resist snapping in hard metal; longer bits reach further but wander more and break more easily if the drill is not held straight. In Europe, metric jobber-length HSS drills are made to DIN 338, and the table below lists overall lengths for common sizes from Starrett's catalogue. Matching inch figures for jobber, stub and taper lengths were not available from a source we could verify, so this page does not give them.

10Which shank does a drill bit need to fit your drill?

A bit's shank must suit the drill's holder: round and three-flat shanks go in a jawed chuck, 1/4 in hex shanks go in an impact driver's quick-change holder, and SDS shanks go only in an SDS rotary hammer. Chuck size names the largest shank the chuck accepts, not the largest hole the drill can make.

That last point corrects a common belief: a 1/2 in drill is not limited to holes of that size. Reduced-shank bits, sometimes called Silver and Deming bits, cut larger holes but have a shank turned down to fit the chuck. Flats ground on a shank, as on three-flat bits and spade bits, are there to stop the bit slipping. Impact-rated bits with a hex shank are made for impact drivers; Milwaukee sells such bits for its drivers. The drill chuck sizes guide lists the capacity range of common keyless chucks.

11How fast should each type of drill bit spin?

Smaller bits spin faster than larger ones, and hard materials need lower speeds than soft ones. Starrett and Engineering ToolBox both publish speed charts on that pattern; the inch chart below is from Engineering ToolBox, and Starrett's metric catalogue chart follows the same pattern for HSS drills in steel, stainless, cast iron and non-ferrous metals.

Starrett also recommends a lubricant when drilling metal, to reduce friction wear, keep the edge sharp and lower the risk of breakage. Wood bits follow the same rule: Forstner and spade bits slow down sharply as their diameter grows. Glass and tile bits sit at the bottom of the range, as noted above.

12Is there a drill bit that cuts sideways?

Ordinary drill bits are made to cut at the tip, not along their sides; a twist bit pushed sideways in the hole will bend or snap rather than cut. Cutters that remove material sideways belong to a different family, such as router bits, which cut with the edges along their length and are guided across the work.

That is why a search for a drill bit router usually ends at a router rather than a drill: spiral router bits look like drill bits but are made for a router's much higher speed and a sideways feed. The guide to router bits that cut sideways explains how those cutters are chosen. Reamers, which enlarge an existing hole to a precise size, are not covered by the sources in our fact base, so this page does not give guidance on them.

13How do you choose the right drill bit, step by step?

These steps narrow the choice from the material to a specific bit.

1. Name the material. Wood, mild steel, stainless, sheet metal, masonry, tile or glass each point to a different bit type in the table above.
2. Pick the bit type. Brad-point, spade, Forstner or auger for wood; twist for general metal; cobalt for stainless; step for sheet; carbide masonry or SDS for concrete; diamond or spear-point for tile and glass.
3. Check the hole size. If the hole is larger than common bits, move to a Forstner bit in wood or a hole saw in other materials.
4. Match the shank to the tool. Round or three-flat for a jawed chuck, hex for an impact driver, SDS for a rotary hammer.
5. Choose the length. Use the shortest length that reaches through the work: stub for accuracy in hard metal, jobber for general use, long-series for deep holes.
6. Set speed and cooling. Lower speed for larger bits and harder materials, lubricant for metal, water for diamond bits.

14Why does a drill bit wander, burn or snap?

Wandering, burning and snapping each trace to a mismatch between bit, material and technique. Ordinary twist drills tend to wander on a flat surface; in metal this is countered with a spotting (pilot) drill, in wood with a brad-point bit, and split points reduce deviation. In metal, a center punch mark gives the tip a place to start; McMaster-Carr's listing for a Starrett punch describes it as stopping the drill wandering. The guide to stopping a drill bit walking goes through each fix.

Burning comes from heat. A Forstner bit run too fast scorches the wood and dulls quickly, and a glass bit run fast overheats. Snapping is most common with brittle bits, carbide and cobalt, when the drill is tipped sideways, and with long bits that flex. A dull bit makes every one of these worse because it needs more feed pressure. If a bit keeps slipping in the chuck instead, the cause is usually at the shank, and flatted shanks exist to resist that slip.

15Where should you go from here?

Once you know the bit type, the next step is usually a size: the drill size chart, the tap drill chart and the pilot hole chart linked above give the exact figure for threads and screws. To see which bits suit a particular drill or driver, the accessory finder filters by tool, and the other how-to guides cover saw blades, router bits and abrasives in the same way.

16Questions readers ask