Product Guides
AIMS Drill Bit Selection Guide: Choose by Material, Application & Cost
A practical guide to selecting the right drill bit for the workpiece you're cutting. Covers HSS, cobalt HSS, solid carbide, carbide-tipped, masonry, tile and glass drill bits, plus jobber, stub, step and SDS sub-types. Includes drill point geometry, coatings, brand selection across Sutton Tools, Bordo and P&N, and AS/NZS/ISO standards relevant to Australian industry.
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Cobalt Drill Bit Guide: HSS-Co Grades, M35, M42 & When to Upgrade
The single most-asked question in any Australian metal-working workshop: "What drill bit do I use for stainless steel?" The answer, ninety percent of the time, is a cobalt drill bit. Understanding why takes a few minutes — and getting the wrong cobalt drill bit (or the right cobalt drill bit but using it incorrectly) is the difference between drilling 304 stainless cleanly all day and replacing burnt bits every five holes. Cobalt drill bits are not a coating. They are not "cobalt-coloured" because of a finish. The cobalt is alloyed into the high-speed steel itself — typically 5% (M35 grade) or 8% (M42 grade) — which raises the steel's hot hardness and lets the cutting edge survive the heat that ordinary HSS can't handle. That's the whole engineering story, and it's why cobalt is the standard for stainless, hardened steel, cast iron and high-tensile bolts. This guide covers what cobalt drill bits actually are, the grade differences (M35, M42, HSS-PM), the materials they're designed for, the technique that makes them last (and the technique that wastes them in five seconds), brand selection in the Australian market, and the cost reality of when cobalt pays back vs staying with premium HSS or upgrading further to solid carbide. For the broader drill bit selection guide covering all materials and bit types, see our Choosing the Right Drill Bit guide and Types of Drill Bits reference. This article focuses specifically on cobalt as a substrate choice. Need another reference chart? Browse the full AIMS Engineering Reference Charts library — drill bit sizes, tap drill, torque, viscosity, GD&T, AS/NZS standards and more. Cobalt Drill Bit Selector — Choose by Job This guide is a working selector tool — not just a reference. Use it to choose the right cobalt drill for your job. Pick your scenario below for a direct path to the right product, or scroll down for the full M35-vs-M42 grade comparison and material-by-material selection. How to use: 1. Pick your scenario 2. View the product 3. Choose your size from the variant selector Stainless Steel Drilling M35 cobalt — workshop standard Sutton D108 View → Heavy-Duty Production M42 cobalt bulk pack Sutton D109 View → 19-pc Metric Cobalt Set 1mm-10mm in case Sutton D109SM2 View → Imperial Cobalt Sizes 1/16" - 1/2" range Sutton D108 View → Hardened Steel (>30 HRC) Black Magic stub — TiAlN coated Sutton D153 View → Premium Coated Cobalt Black Magic jobber TiAlN Sutton D169 View → Browse Full Cobalt Range All sizes + grades + sets Collection View → Compare to HSS / Carbide Decision guide Selection Guide View → Cobalt drills are the right answer for stainless steel, hardened steel (up to ~50 HRC), titanium, high-tensile bolts, and anything where HSS bright drills work-harden and snap. For mild steel + occasional drilling, regular HSS is more economical (see Drill Bit Selection Guide). Need help? Call (02) 9773 0122. Jump to: M35 vs M42 vs HSS / Carbide Stainless Hardened Steel Speed/Feed/Fluid Identification Brands Cost Analysis Related Selectors AIMS Top Picks — Pick the Right Cobalt Drill Bit Cobalt (HSS-Co, typically M35 or M42) drills bridge the gap between HSS jobber and solid carbide — better than HSS on tough materials (stainless, work-hardened steel), cheaper than carbide, more forgiving on hand-held + manual machines. AIMS stocks Sutton's professional cobalt range plus Bordo value-tier cobalt. Call (02) 9773 0122 for size advice. Workshop Default — Sutton D108 Range Application AIMS recommendation Why this one Workshop default — metric sizes Sutton D108 Cobalt Jobber Metric The AU workshop standard cobalt drill. Colour-tempered for visual identification. 1.0–13.0mm metric range Imperial workshop sizes Sutton D108 Cobalt Jobber Imperial Same D108 in imperial (1/16"–1/2") — for older drawings + US machinery work Heavy duty production (bulk pack) Sutton D109 Heavy Duty Cobalt Bulk Pack D109 = upgraded cobalt content for production volume. Bulk pack pricing for fab shops Left-hand cobalt (stud extraction) Sutton D202 Left-Hand Cobalt Jobber Left-hand cut direction — for broken stud extraction. The cobalt + reverse rotation combo backs out broken bolts as it drills Bordo Value-Tier Cobalt Application AIMS recommendation Why this one Bordo 2011 series (workshop value) Bordo HSS Cobalt Jobber 2011 Series Bordo's professional cobalt range — workshop value tier vs Sutton D108. Mid-price quality Bordo 2010 series Bordo HSS Cobalt Jobber 2010 Series Entry-level Bordo cobalt — for occasional cobalt work where premium tier isn't justified When to Step Up from Cobalt to Carbide Cobalt is the right answer for ~80% of stainless, work-hardened and heat-treated steel work. Step up to solid carbide when you're doing PRODUCTION volume (50+ holes/day in tough material), or when the material is over 40 HRC (hardened tool steel, Inconel, hardened bearing steel). For carbide drilling, AIMS stocks Sutton D300/D304/D306/D310/D323 VHM TiCN/AlCrN range — see the Drill Bit Selection Guide. Buying tip from AIMS: Cobalt drill bits look identical to HSS — the cobalt is alloyed throughout, not coated. Sutton's D108/D109 use a heat-temper colour as a visual identifier. If your drill isn't colour-tempered or marked "HSS-Co" / "M35" / "M42", it's probably HSS, not cobalt. Use cobalt for stainless 304/316 (drills 2-3× longer than HSS) and for any material where HSS work-hardens. For mild steel, HSS jobber (Sutton D101/D102 Bullet) is still the more economical choice.What is a cobalt drill bit? A cobalt drill bit is a high-speed steel (HSS) drill bit with cobalt alloyed into the steel itself. The cobalt is part of the steel — not a surface treatment, not a coating. You cannot scrape the cobalt off; it is the steel. The two main cobalt grades are designated by their cobalt content: M35 grade — 5% cobalt. The standard cobalt drill bit. Significantly better than plain HSS in heat-generating cuts. The default upgrade choice from M2 HSS for stainless steel and most hardened metals. M42 grade — 8% cobalt. The premium cobalt grade. Higher hot hardness still, longer life in stainless and very hard steels. About 30–40% more expensive than M35; chosen for production-volume work or particularly demanding materials. The cobalt addition raises the steel's red hardness — the temperature at which the steel begins to soften and lose its cutting edge. Standard M2 HSS softens around 600°C; M35 cobalt holds its edge to about 650°C; M42 to about 700°C. That additional 50–100°C is the difference between cutting cleanly through stainless steel and burning the cutting edge off in three holes. Visually, cobalt drill bits typically have a duller, more golden or bronze tint than bright HSS — but colour alone is not a reliable indicator. Cheap drill bits sometimes use surface colouring to imply cobalt content that doesn't exist. The only reliable indicator is the manufacturer's marking and the brand reputation behind it. M35 vs M42 vs HSS-PM — cobalt grade selection Grade Cobalt content Red hardness Best for Cost (vs M2 HSS) M2 HSS (baseline) 0% ~600°C Mild steel, aluminium, brass, copper, plastics, timber 1× M35 (5% Co) 5% ~650°C Stainless 304/316, hardened steel to ~30 HRC, cast iron, high-tensile bolts up to grade 8.8 ~1.5–2× M42 (8% Co) 8% ~700°C Heavy stainless production, 17-4 PH, hardened steel to ~45 HRC, high-tensile bolts grade 10.9, abrasive materials ~2.5–3× HSS-PM (Powder Metallurgy HSS, e.g. ASP 2030, T15) 5–10% (varies) ~700°C, plus toughness boost Same materials as M42, plus very interrupted cuts and shock-loaded applications. Premium specialty. ~3–5× Solid carbide (next step up) — ~900°C+ Hardened steel above 45 HRC, titanium, abrasive composites, production CNC ~5–10× M2 HSS The practical selection rule: Drilling stainless 304 or 316 occasionally in a workshop? Use M35. The cost premium over M2 HSS is small; the performance gain is enormous. Production drilling in stainless, repetitive work, or material harder than 304? M42. The extra 30–40% cost is paid back many times over in tool life. Hardened steel above 45 HRC, or any application where M42 still struggles? Solid carbide. Cobalt's red hardness ceiling has been reached. HSS-PM is specialist territory — interrupted cuts in hardened material, shock-loaded applications, high-precision sharpenability. Most workshops never need it. Cobalt vs HSS, cobalt vs carbide — where each fits Three substrates, three different sweet spots. The choice isn't "best material" — it's matching the substrate to the application. Property M2 HSS M35/M42 cobalt Solid carbide Hardness ~63–66 HRC ~67–70 HRC ~89–93 HRA (≈75–80 HRC) Hot hardness ceiling 600°C 650–700°C 900°C+ Toughness (resistance to chipping) High Slightly lower than M2 Brittle — chips easily Resharpenable Yes (basic grinder) Yes (with care) Specialist regrinding only — not economical Cost (10 mm twist drill) ~$8–15 ~$15–35 (M35) or $25–50 (M42) ~$50–120 Best for Mild steel, soft non-ferrous, timber, plastics Stainless, hardened steel, high-tensile bolts, cast iron Above ~45 HRC, titanium, hardened production work Worst for Stainless (work-hardens, burns out) Above ~45 HRC (cobalt softens before cutting) Interrupted cuts (shatters), DIY hand drilling (snaps) The pattern: as you move from M2 HSS → cobalt → carbide, hardness goes up but toughness goes down. Cobalt sits in a sweet middle position — hard enough for stainless and hardened steel up to about 45 HRC, tough enough to survive hand drilling and interrupted cuts that would shatter solid carbide. For most Australian workshop drilling needs above mild steel, cobalt is the right answer. For the analogous decision on end mills, see our Carbide vs HSS End Mill deep-dive — the substrate logic is similar but the application differences (rotational drilling vs side-cutting milling) shift the breakpoints. Stainless steel: the cobalt sweet spot Austenitic stainless steel — 304 and 316, the most common AU industry grades — has one specific behaviour that defeats ordinary HSS drill bits and makes cobalt the right choice: work-hardening under heat and pressure. When a drill bit cuts stainless steel, friction generates heat at the cutting edge. The stainless steel surface beneath the cutting edge responds to this heat by becoming harder — a layer typically 0.05–0.2 mm thick that's measurably harder than the parent material. If the drill bit can't cut through this hardened layer, it rubs instead of cuts; rubbing generates more heat; more heat creates a deeper hardened layer; and the bit either burns its cutting edge off (HSS) or simply skates across a now-hardened surface. Cobalt's higher red hardness lets the cutting edge stay sharp at the temperatures that work-harden stainless. The bit cuts through the work-hardened layer faster than a new layer forms. Combined with correct technique, cobalt drills stainless cleanly. The same cobalt-HSS logic applies up the scale: for larger-diameter structural stainless holes that exceed twist drill capacity (16-50mm+), the cobalt-grade annular cutter in a magnetic drill uses the same red-hardness advantage with the same technique rules — slow RPM relative to mild steel, continuous coolant, solid steady feed, never pause mid-cut. The stainless steel work-hardening warning If you drill stainless steel at high RPM, with light pressure, or with pauses mid-hole, you create a work-hardened zone that even a premium M42 cobalt cannot drill through. The correct technique is the opposite of intuition: slow speed, firm consistent pressure, continuous cutting fluid, no pausing once started. Pecking — lifting the bit and restarting — is the classic failure mode. Once you create the hardened zone, the drill is finished and probably so is the bit. Forum reality: r/metalworking's "Can't for the life of me drill through stainless steel" thread (110+ comments) is almost entirely diagnoses of work-hardening from incorrect technique. The correct stainless steel drilling technique: Slow speed. A 6 mm cobalt bit in 304 stainless wants approximately 200–400 RPM, not 1,000+. A 12 mm bit wants 60–120 RPM. The general rule: about one-third the speed you'd run for mild steel. Firm consistent pressure. Push the bit hard enough that it's continuously cutting (chips coming off, not dust). Light pressure equals rubbing equals work-hardening. Continuous cutting fluid. Even a few drops of thread-cutting oil or dedicated stainless fluid (Trefolex, Tap Magic) makes a substantial difference in bit life and finish quality. Soluble oil also works on benchtop drilling. Don't peck or pause. Once the bit is engaged, keep cutting until the hole is through. Lifting the bit creates a perfect work-hardened ring at the depth you stopped — then the next cut hits hardened material before any fresh cutting can start. Start with a centre punch. Cobalt bits don't like wandering; a centre-punched divot keeps the bit on target from the first revolution. Use a sharp bit, not a tired one. A dull cobalt bit on stainless is just creating heat and hardening the material. Resharpen or replace. For full speeds and feeds reference across all material/bit combinations, see our Cutting Speeds and Feeds Chart. For cutting fluid selection by application, see our Cutting Fluids Guide. Hardened steel: cobalt's outer limit Cobalt drill bits handle hardened steel up to approximately 45 HRC reliably with M42 and 30–35 HRC with M35. Above that, you're approaching the cobalt ceiling and solid carbide is the appropriate next step. Material hardness Recommended substrate Notes Up to ~25 HRC (mild and medium-tensile steel) M2 HSS Cobalt is overkill — premium HSS handles this fine 25–35 HRC (high-tensile bolts grade 8.8, some heat-treated steel) M35 cobalt Standard cobalt territory 35–45 HRC (heat-treated tool steel, hardened spring steel, grade 10.9 bolts) M42 cobalt Slow speed and good fluid mandatory 45–55 HRC (hardened tool steel, dies) Solid carbide (TiAlN coated) Cobalt softens at the cutting temperatures generated; carbide handles it 55+ HRC (case-hardened surfaces, hardened bearings) Solid carbide or specialty (CBN grinding) Drilling becomes very difficult; sometimes annealing is required first The "stuck bolt" scenario. Snapped grade 8.8 bolts, broken taps, hardened studs — the classic AU workshop "I need to drill out something hard" job. Forum consensus from Practical Machinist and Reddit r/Machinists is consistent: M42 cobalt is the standard first attempt; if M42 won't bite, the bolt is harder than 45 HRC and it's solid carbide territory. For broken tap removal specifically, see our Broken Tap Removal Guide. Cast iron, high-tensile bolts and abrasive materials Beyond stainless and hardened steel, cobalt drill bits are the right choice for several other Australian-workshop materials: Cast iron — abrasive but not particularly hard. Cobalt's wear resistance pays off; the chip is short and crumbly which doesn't load the flutes. Drill cast iron dry — adding cutting fluid creates an abrasive paste that wears the bit faster than dry cutting. M35 is usually sufficient. High-tensile bolts (grade 8.8, 10.9, 12.9) — bolt grades 8.8 and above are heat-treated and run 30–45 HRC. Cobalt is the appropriate substrate; M42 for the harder grades. Drill slowly with cutting fluid, don't peck. Spring steel and music wire — heat-treated, 50–55 HRC. M42 cobalt occasionally works at very low speeds; solid carbide is more reliable. Inconel and high-temperature alloys — work-hardens severely, generates high heat. M42 cobalt is workable for one-off holes; production volume = solid carbide with appropriate coatings. Titanium and titanium alloys — low thermal conductivity means heat stays in the bit. M42 cobalt is marginal; solid carbide with AlCrN or similar coating is the standard production choice. Abrasive composites (fibreglass, carbon fibre) — pure abrasive wear regardless of hardness. Solid carbide or PCD-tipped is the long-life choice; cobalt works for small volumes. Speed, feed, and cutting fluid for cobalt Cobalt's hot-hardness advantage only delivers if you give the bit the conditions to use it. Wrong speed and feed make a $30 cobalt drill bit perform like a $5 HSS — burning out fast and leaving a rough hole. Material Cobalt cutting speed (V_c, m/min) RPM for 6 mm bit RPM for 10 mm bit Cutting fluid Stainless 304 15–22 800–1,170 480–700 Trefolex / Tap Magic / sulphurised cutting oil Stainless 316 12–18 640–960 380–570 Same — 316 needs slightly slower Hardened steel 30–40 HRC 10–15 530–800 320–480 Sulphurised oil, slow steady feed Cast iron (grey) 25–35 1,330–1,860 800–1,110 Dry — no fluid Mild steel (cobalt overkill) 30–45 1,600–2,400 950–1,430 Soluble oil or none for short jobs Aluminium (cobalt overkill but works) 60–100 3,180–5,300 1,910–3,180 WD-40 or kerosene The general rule for cobalt vs HSS speeds: cobalt runs at the same speed as HSS in mild steel, about 1.5× HSS speed in stainless (because HSS shouldn't really be used in stainless), and well below HSS speed in hardened material. Slower than you might think — many DIY drilling failures come from running cobalt at the same speed you'd use for mild steel HSS. Feed rate matters as much as speed. Light feed (low pressure on a hand drill, low feed setting on a drill press) creates rubbing rather than cutting and burns the bit. A cobalt drill bit wants firm, consistent feed pressure that produces continuous chips — a chip should be coming out of the hole every revolution. Hand drill vs drill press technique Cobalt drill bits work in both, but the technique differs. On a drill press: set the speed correctly for the material and bit diameter; clamp the work; apply firm continuous feed; use cutting fluid liberally. Drill press technique is mostly about the setup — once the speed and clamping are right, the cutting itself is straightforward. In a hand drill (battery or corded): the challenge is the operator. You need to maintain consistent feed pressure, hold the drill straight (no wobbling), and stop cleanly through the back side of the work. Hand-drilling stainless with cobalt is achievable but requires: The drill set to low speed — most cordless drills have a Hi/Lo selector. Use Lo. If yours has variable trigger, run it at maybe 30–40% trigger pull. A centre punch on the marked spot before starting (cobalt bits hate wandering) Both hands on the drill, body weight behind it, feeding firmly A squirt of cutting fluid applied before starting and re-applied if you stop No stopping mid-hole. If you must stop, lift the bit clear and re-apply fluid before continuing. Watch the chip colour. Bright silver chips = correct technique. Blue or brown chips = too much heat — slow down or apply more fluid. Hand-drilling thicker stainless (above 6 mm) with a small cobalt bit is hard work. For repetitive work in stainless, a drill press or magnetic base drill makes the job dramatically easier. Cobalt drill bit identification — markings and what to look for How to tell whether a drill bit is genuinely cobalt — and what grade: Manufacturer marking. Premium cobalt drill bits are laser-marked or stamped with the grade designation (M35, M42, HSS-Co5, HSS-Co8). Sutton, Bordo, Tivoly, Dormer, Cleveland, Triumph and other premium brands all mark their cobalt clearly. Unmarked or vaguely-marked drill bits should be assumed to be standard HSS regardless of seller claims. Standards markings. Cobalt drill bits to DIN 338 = jobber-length cobalt twist drill DIN 1869 or DIN 340 = long series cobalt DIN 1897 = stub series cobalt The DIN number is followed by the grade: HSS-Co5, HSS-Co8 Colour is unreliable. Genuine cobalt is typically a duller gold/bronze tint than bright HSS, but cheap drill bits can be artificially coloured to look the same. Don't rely on colour alone. Magnetism. Cobalt drill bits remain magnetic (it's still steel, just alloyed). Solid carbide drill bits are barely magnetic — if a "carbide" drill bit sticks to a magnet strongly, it's likely not solid carbide. Brand reputation. A Sutton-marked, Tivoly-marked or Dormer-marked cobalt drill bit is genuine cobalt at the stated grade. An unbranded or generic-branded "cobalt" drill bit on eBay or marketplace at one-third the price of premium is a quality risk regardless of marketing claims. The Practical Machinist thread "Where can you get a REAL M42 cobalt drill?" exists because so much "M42" tooling on the cheap end of the market is mis-marked. Brand selection in the Australian market Sutton Tools (manufactured in Thomastown, Victoria) — Australia's premium cobalt drill bit manufacturer. Comprehensive M35 and M42 ranges across jobber, stub and long-series formats. The standard recommendation for most Australian workshops. AIMS stocks the Sutton range — see the Sutton Tools collection. Bordo — Australian-distributed range, strong on M35 cobalt and HSS. Good value for hand-drill use and moderate workshop volumes. AIMS-stocked. Tivoly (France) — premium European cobalt manufacturer, available in AU through specialist tool distributors. Excellent quality, premium price. Dormer (UK/Sweden, now Dormer Pramet) — premium European brand with full cobalt range. Available through industrial distributors. Other premium brands available in AU on order: Cleveland (USA), Triumph (USA), OSG (Japan), Mitsubishi (Japan), YG-1 (South Korea — value premium). Avoid: unbranded cobalt drill bits on eBay, marketplace listings, or budget retailers at unrealistic prices. Forum-validated reality: cheap "M42 cobalt" sets often turn out to be standard HSS coloured to look like cobalt, or M35 sold as M42, or cobalt content well below the marked grade. A premium HSS bit ($10) typically outperforms a $5 fake-cobalt every time. Cheap "cobalt" quality variance warning Budget drill bit sets marketed as "cobalt" or "M42" frequently fail testing — wrong cobalt content, wrong grain structure, or no cobalt at all. The Practical Machinist thread "Where can you get a REAL M42 cobalt drill?" runs to many pages of disappointed buyers. If a cobalt drill bit set costs less than premium HSS, scepticism is warranted. Stick to brands you can verify: Sutton, Bordo, Tivoly, Dormer, Cleveland, Triumph, OSG, Mitsubishi, YG-1. Cost reality: when does cobalt pay back vs premium HSS? The premium for genuine cobalt over premium HSS is real but smaller than people assume: Bit (10 mm jobber, premium AU brands) Approx AU price (single bit) Multiplier M2 HSS (premium, e.g. Sutton/Bordo) ~$8–15 1× M2 HSS with TiN coating (gold) ~$12–20 ~1.3× M35 cobalt (5%, e.g. Sutton M35) ~$15–25 ~1.5–2× M42 cobalt (8%, premium) ~$25–45 ~2.5–3× HSS-PM specialty (e.g. ASP 2030) ~$40–80 ~4–5× Solid carbide (TiAlN-coated) ~$50–120 ~5–8× The payback math: A premium HSS bit drilling stainless will drill maybe 5–10 holes before the cutting edge is gone, then needs resharpening or replacement. A premium M35 cobalt in the same stainless will drill 50–100 holes before resharpening is needed. The cobalt's life is roughly 10× longer in stainless. At 1.5–2× the bit cost, cobalt pays back the upgrade cost on the second hole and everything after that is pure savings. In materials where HSS works fine (mild steel, aluminium, brass, timber), cobalt is overkill — you're paying 1.5–2× for performance you don't need. Run HSS for the easy materials and keep cobalt for stainless, hardened steel, and the genuinely hard materials. Build a mixed kit: the right Australian workshop drill bit kit is a mix — premium HSS in common sizes for general work, plus M35 cobalt in 4–10 mm sizes for stainless and hardened material work. Add M42 for production-volume stainless. Solid carbide for jobs where cobalt has reached its limit. Common mistakes that kill cobalt drill bits early Cobalt drill bits should last a long time. When they fail prematurely, it's almost always one of these mistakes: Running too fast. The most common error. Cobalt's heat-resistance advantage doesn't help if you generate so much heat that even cobalt's ceiling is exceeded. In stainless, slower than your instinct says. Pecking — lifting and restarting. Each lift creates a work-hardened ring; the next cut hits the hard ring and burns out the cutting edge. Once you start, finish. No cutting fluid. Stainless and hardened steel need fluid. A few drops of thread-cutting oil makes the difference between a bit that lasts and a bit that burns out. Light feed pressure. Rubbing instead of cutting work-hardens the material and overheats the bit. Push firmly enough to be cutting continuously. Using cobalt where HSS would do. Not a failure, just waste — you're consuming expensive bits on jobs that don't need them. Using HSS or "cobalt"-marked-cheap-bit on stainless. Burns out, gets blamed on the work, gets replaced with another cheap bit, repeats. The real fix is genuine cobalt. Drilling cast iron with cutting fluid. Counter-intuitive but true — fluid + iron dust creates abrasive paste. Drill cast iron dry. Not centre-punching. Cobalt bits wander if not started in a punch mark. Wandered bits make oversized, off-centre holes and stress the cutting edge. Letting the bit stop in the hole. Battery dying mid-cut, drill press tripping, hand drill clutch slipping — all create the work-hardening trap. Buying unverified cheap "cobalt" bits. If it's not genuine, the cobalt benefit isn't there regardless of the marking. Cobalt drill bits at AIMS Industrial AIMS stocks Sutton M35 and M42 cobalt drill bits (Australian-made), Bordo M35 cobalt, and selected premium imports. Browse the full range in our dedicated Cobalt Drill Bits collection. For other drill bit types and the broader cutting tool range: Jobber Drill Bits collection — HSS jobber-length twist drills for general metal and timber work Sutton Tools collection — full Sutton range including HSS, cobalt and solid carbide drill bits, taps, reamers and end mills Carbide Drill Bits collection — for the next-step upgrade above cobalt's limit (hardened steel above 45 HRC, titanium, abrasive composites) For specific cobalt grades, sizes, or premium imports we don't show online, call us on (02) 9773 0122 or use our contact page. We can source most premium cobalt and carbide drill bits available in the Australian market. For the broader drill bit selection guide covering all materials, see our Choosing the Right Drill Bit Guide and Types of Drill Bits reference. When a fastener won't come loose with normal effort, walk through the full escalation in our How to Remove Stuck Bolts & Nuts guide — penetrant through to drill-out and weld-on. Related AIMS Selectors This guide complements AIMS's other drilling selectors. Use them together for complete coverage: Drill Bit Size Selector — every metric drill diameter linked to AIMS-stocked SKU. Drill Bit Selection Guide — broad guide on HSS vs cobalt vs carbide for general drilling. Tap Drill Size Selector — for threading work, gives you the tap + matching drill SKU. Tap & Die Selection Guide — companion guide on tap selection (also cobalt for stainless). HSS vs Carbide End Mill — when carbide is worth the cost (same material principle as drills). Cutting Speeds & Feeds Reference — RPM and feed rate for cobalt drilling by material. Cutting Tool Materials — HSS, cobalt, carbide grades compared. Cutting Tool Coatings — TiN, TiAlN, AlCrN, when each matters for cobalt drills. Cutting Tool Troubleshooting — walking drills, oversize holes, snapped tips. Or browse the full cobalt drill bits range + jobber drill bits + reduced shank for larger sizes — Sutton primary, Bordo and P&N alternates, in stock for next-day Australia-wide dispatch from our Milperra warehouse.Frequently Asked Questions What is the difference between HSS and cobalt drill bits? Cobalt drill bits are high-speed steel with cobalt alloyed into the steel itself — typically 5% (M35) or 8% (M42). The cobalt isn't a coating; it's part of the steel. The cobalt addition raises the steel's red hardness (the temperature at which the cutting edge begins to soften) from about 600°C for plain M2 HSS to 650–700°C for cobalt grades. This extra heat resistance makes cobalt the right choice for stainless steel, hardened steel, cast iron and high-tensile bolts where ordinary HSS burns the cutting edge off in a few holes. Are cobalt drill bits worth the extra cost? For drilling stainless steel, hardened steel, cast iron, or high-tensile bolts — yes, by a wide margin. A cobalt drill bit in stainless typically lasts 5–10× longer than HSS at 1.5–2× the price, paying back the upgrade cost on the second hole. For drilling mild steel, aluminium, brass, or timber where HSS works fine, cobalt is overkill — premium HSS is a smarter spend. Build a mixed kit: HSS for general work, cobalt M35 for stainless and hardened material, M42 for production-volume hard work, solid carbide for above 45 HRC. What is the difference between M35 and M42 cobalt drill bits? M35 contains 5% cobalt; M42 contains 8% cobalt. The higher cobalt content gives M42 a slightly higher red hardness (~700°C vs ~650°C for M35), longer tool life in stainless and hardened steel, but at 30–40% higher price. For occasional stainless drilling, M35 is sufficient and cost-effective. For production-volume stainless work or hardened steel above 35 HRC, M42 pays back the cost premium through longer tool life. Above 45 HRC, both are at their limit and solid carbide is the right next step. What is the best drill bit for stainless steel? A genuine M35 or M42 cobalt jobber drill bit from a verified premium brand (Sutton, Bordo, Tivoly, Dormer), used with correct technique: slow speed (about one-third of mild steel speed), firm consistent feed pressure, continuous cutting fluid, and no pausing once started. The combination of cobalt substrate plus correct technique handles 304 and 316 stainless cleanly. Cheap "cobalt" drill bits on eBay or budget retailers frequently fail because the cobalt content is below the marked grade or absent entirely. Why does my drill bit keep burning out in stainless steel? Almost always one of: running too fast (stainless wants slow speed — about one-third of mild steel RPM); pecking (lifting and restarting creates a work-hardened zone); insufficient cutting fluid (stainless needs continuous fluid); light feed pressure (rubbing instead of cutting work-hardens the material); or using HSS instead of cobalt. The mechanism is stainless steel's work-hardening behaviour — under heat and friction the surface gets harder, and if your bit can't cut through the hardened layer faster than new layers form, it rubs and burns. Fix: cobalt M35 or M42, slow speed, firm feed, continuous fluid, no pausing. Is M42 cobalt better than carbide for hardened steel? Up to about 45 HRC: M42 cobalt is the right choice. Cobalt is much tougher than carbide and survives the interrupted cuts and slight misalignment that hand drilling creates. Above 45 HRC: solid carbide takes over because cobalt softens at the cutting temperatures generated. The crossover point depends on how hard the material is and how production-grade your setup is — for occasional hand-drill work, M42 cobalt can stretch up to 50 HRC if you go slow with fluid; for production work, carbide above 45 HRC. Can cobalt drill bits be resharpened? Yes — cobalt is just alloyed HSS, so it sharpens on the same equipment as standard HSS drill bits. A drill bit sharpener (Drill Doctor, Tradesman) handles cobalt fine; a bench grinder with the right wheel and a steady hand also works. The cutting edge geometry matters: 135° split-point is the modern standard for stainless and metal drilling, much better than the older 118° tip. Cobalt holds a sharp edge well after regrinding. The regrindability is part of the cost story — a $25 cobalt bit with two regrinds at $5 each delivers $35 total cutting capacity. Are cobalt drill bits the same as cobalt-coated drill bits? No — and the distinction matters. Genuine cobalt drill bits have cobalt alloyed into the steel itself (5% for M35, 8% for M42). The cobalt is part of the steel and stays there even after resharpening. "Cobalt-coated" or "cobalt-finish" drill bits are HSS with a thin surface treatment — the coating wears off in normal use and is gone after the first regrind. Marketing language sometimes blurs this distinction; check for the M35 or M42 grade marking, and the brand reputation, to verify genuine cobalt. What cutting fluid should I use for drilling stainless with cobalt? For stainless steel: a sulphurised cutting oil is the standard recommendation — Trefolex, Tap Magic, Rocol RTD, or similar dedicated thread-cutting and stainless drilling fluids. Even general-purpose soluble oil or a few drops of motor oil is better than nothing. For hardened steel: same — sulphurised oil. For cast iron: nothing — drill dry, fluid creates abrasive paste. For mild steel: optional, but soluble oil extends tool life. For aluminium: WD-40 or kerosene work well; never sulphurised oil (stains aluminium). See our Cutting Fluids Guide for the full breakdown. Why are some cobalt drill bits gold-coloured and others silver? The colour difference is mostly cosmetic. Bright silver/grey is uncoated genuine cobalt — the natural colour of HSS-Co. Gold-tinted cobalt bits have a thin TiN (titanium nitride) coating over the cobalt substrate, intended to add slightly more wear resistance. The TiN coating wears off the cutting edge in normal use, after which the bit performs identically to uncoated cobalt. The colour is not a reliable indicator of cobalt grade — check the manufacturer's marking (M35, M42) for the actual grade. Cheap drill bits sometimes use gold colouring to imply cobalt content that doesn't exist. Can cobalt drill bits drill through hardened bolts? Yes — that's exactly what they're designed for. Grade 8.8 high-tensile bolts run about 30 HRC; grade 10.9 about 35 HRC; grade 12.9 about 40 HRC. M35 cobalt handles 8.8 cleanly; M42 cobalt handles up to 10.9 reliably and 12.9 with care. Above grade 12.9, you're approaching solid carbide territory. Technique matters: slow speed, cutting fluid, firm feed, no pecking. For broken bolt extraction specifically (snapped studs in tapped holes), see our broken tap removal guide — same principles apply for studs. What is HSS-PM and is it worth the extra cost over M42? HSS-PM stands for high-speed steel — powder metallurgy. The steel is produced from atomised powder rather than conventional ingot casting, giving a more uniform grain structure and higher toughness at the same hardness. Common designations include ASP 2030, T15, M48-PM. HSS-PM holds an edge as well as M42 cobalt with better toughness, particularly in interrupted cuts and shock-loaded applications. The cost premium is significant — typically 3–5× M2 HSS — and most workshops will never need it. Specialist territory for production-volume hard milling and drilling. How fast should I run a cobalt drill bit? Significantly slower than you'd run HSS in mild steel. For 304 stainless with a 6 mm cobalt bit: 800–1,170 RPM. For 10 mm: 480–700 RPM. For 12 mm in 316 stainless: 320–480 RPM. For hardened steel: lower again — about half those numbers. The general rule for cobalt: about one-third the speed of mild steel for stainless, half the speed for hardened material, and same speed as HSS for mild steel and aluminium. See our Cutting Speeds and Feeds Chart for the full reference table. Are budget cobalt drill bit sets worth buying? Generally no. The Practical Machinist thread "Where can you get a REAL M42 cobalt drill?" runs to many pages of buyers reporting that budget cobalt sets test out as standard HSS or low-cobalt M35 sold as M42. The cost saving is real (~30–50% off premium prices) but tool life is often half or less of premium cobalt — wiping out the saving on the first major job. A premium M35 from Sutton, Bordo, Tivoly or Dormer at $15–25 is a smarter spend than a $40 unbranded "M42" set with 13 sizes that may or may not actually be cobalt. Quality variance in cheap drill bit sets is huge; brand reputation is the only reliable check. What is a "split point" cobalt drill bit and why does it matter? A split-point drill bit has a small secondary cutting edge ground into the chisel point at the tip — converting the chisel from a wedge that pushes material aside into a cutting edge that cuts material away. The split point is sharper, starts cleanly without wandering, and reduces feed pressure required. For stainless steel and hardened material drilling, 135° split-point geometry is the standard recommendation — it cuts cleanly with less heat generation than the older 118° tip. Most premium cobalt drill bits come split-point as standard. If you're choosing between split-point and standard 118° cobalt for stainless work, choose split-point. For complete metric bolt sizing (M3-M24) with thread pitch and head dimensions, see our Metric Bolt Size Guide. Need sutton tools? Browse the AIMS range at sutton tools.
Read moreMorse Taper Guide: MT1-MT6 Sizes & Compatibility
Morse Taper Sizes: Complete MT0 to MT7 Dimension Reference — Quick Reference The table below lists all standard Morse taper dimensions to DIN 228 Part 1 / ISO 296. These dimensions are identical across all compliant tooling regardless of country of manufacture — a Sutton MT3 drill shank will fit any MT3 socket, whether the machine is Australian, German or. Size Large End Dia (mm) Small End Dia (mm) Length (mm) Taper Ratio Included Angle Angle from CL MT0 9.045 (0.356") 6.401 (0.252") 50.8 (2.00") 1:19.21 2.981 deg 1.491 deg MT1 12.065 (0.475") 9.373 (0.369") 53.5 (2.13") 1:20.05 2.857 deg 1.429 deg MT2 17.780 (0.700") 14.529 (0.572") 64.3 (2.56") 1:20.02 2.861 deg 1.431 deg MT3 23.825 (0.938") 19.762 (0.778") 81.0 (3.19") 1:19.92 2.875 deg 1.438 deg MT4 31.267 (1.231") 25.908 (1.020") 102.0 (4.06") 1:19.25 2.975 deg 1.488 deg MT4.5 38.100 (1.500") 32.156 (1.266") 114.3 (4.50") 1:19.23 2.979 deg 1.489 deg MT5 44.399 (1.748") 37.465 (1.475") 132.0 (5.19") 1:19.00 3.014 deg 1.507 deg MT6 63.348 (2.494") 53.746 (2.116") 184.0 (7.25") 1:19.18 2.985 deg 1.493 deg MT7 83.058 (3.270") 69.850 (2.750") 254.0 (10.00") 1:19.23 2.979 deg 1.489 deg What is a Morse Taper? A Morse taper (MT) is a standardised self-holding taper used to secure cutting tools, drill chucks, centres and other accessories inside the spindles of lathes, drill presses and milling machines. The male taper — on the tool or arbor shank — seats inside a matching female socket in the machine spindle or tailstock quill. Friction alone locks the two surfaces together. No drawbar, no fastener, no thread. The system was developed by Stephen A. Morse of New Bedford, Massachusetts, around 1864. Morse was a twist drill manufacturer and needed a reliable, quick-change method to mount drill shanks in machine spindles. His solution — a gently tapered shank with a very specific angle — proved so effective that it was adopted across the industry within a generation. Today it is the dominant taper standard for drill presses and lathe tailstocks worldwide, used in workshops from Wollongong to Wroclaw. The taper comes in eight sizes: MT0 through MT7 (with the rare MT4.5 bringing the total to nine). Larger numbers mean larger diameter and length. MT2 and MT3 are by far the most common sizes in Australian trade and industrial workshops. The designations are also written as 2MT, 3MT, MK2, or Morse No. 2 — all mean the same thing. How Does a Morse Taper Work? The self-holding mechanism relies on the relationship between the taper angle and friction. The included angle of a Morse taper is approximately 3 degrees (about 1.5 degrees from the centreline — see the full dimension table in the next section). Steel-on-steel friction has a friction angle of roughly 6 to 8 degrees. Because the taper angle is comfortably below the friction angle, the mating surfaces wedge together and cannot release under axial load alone. The harder you push the tool into the socket, the more firmly it locks. This is what "self-holding" means. Compare this to a self-releasing taper like the R8 (used on Bridgeport milling machines). The R8 has a steeper angle — steep enough that cutting forces would cause it to back out of the spindle without a drawbar pulling it from above. The Morse taper angle is shallow enough that this cannot happen under normal axial loading. The tang is for ejection only. The flat tang at the small end of a Morse taper shank fits into a corresponding slot in the socket. Many machinists assume the tang transmits torque — it does not. The friction between the tapered surfaces is what prevents the tool rotating. The tang's sole purpose is to give the drift key something to push against when you need to eject the tool. Applying torque through the tang is a reliable way to twist it off. Drill shanks that have had their tangs broken off — a common workshop occurrence — can still be used in sleeves designed for that purpose, called "tang-free" sockets. Morse Taper Sizes: Complete MT0 to MT7 Dimension Reference The table below lists all standard Morse taper dimensions to DIN 228 Part 1 / ISO 296. These dimensions are identical across all compliant tooling regardless of country of manufacture — a Sutton MT3 drill shank will fit any MT3 socket, whether the machine is Australian, German or Japanese. All metric dimensions are millimetres. Imperial equivalents in brackets. Size Large End Dia (mm) Small End Dia (mm) Length (mm) Taper Ratio Included Angle Angle from CL MT0 9.045 (0.356") 6.401 (0.252") 50.8 (2.00") 1:19.21 2.981 deg 1.491 deg MT1 12.065 (0.475") 9.373 (0.369") 53.5 (2.13") 1:20.05 2.857 deg 1.429 deg MT2 17.780 (0.700") 14.529 (0.572") 64.3 (2.56") 1:20.02 2.861 deg 1.431 deg MT3 23.825 (0.938") 19.762 (0.778") 81.0 (3.19") 1:19.92 2.875 deg 1.438 deg MT4 31.267 (1.231") 25.908 (1.020") 102.0 (4.06") 1:19.25 2.975 deg 1.488 deg MT4.5 38.100 (1.500") 32.156 (1.266") 114.3 (4.50") 1:19.23 2.979 deg 1.489 deg MT5 44.399 (1.748") 37.465 (1.475") 132.0 (5.19") 1:19.00 3.014 deg 1.507 deg MT6 63.348 (2.494") 53.746 (2.116") 184.0 (7.25") 1:19.18 2.985 deg 1.493 deg MT7 83.058 (3.270") 69.850 (2.750") 254.0 (10.00") 1:19.23 2.979 deg 1.489 deg Note on MT4.5: This size exists but is genuinely rare — you are unlikely to encounter it outside of certain older imported lathes. If you think you have an MT4.5, double-check against both MT4 and MT5 before ordering tooling. A note on imperial users: Older Australian machinery, particularly lathes manufactured before the mid-1970s metrication period, will often have imperial-era documentation that refers to Morse tapers by their original inch dimensions. The taper itself is unchanged — it is the same physical socket. The dimension table above includes both metric and imperial values for this reason. Which Machines Use Which Morse Taper? The Morse taper number is determined by the machine's spindle size, which is in turn determined by the machine's capacity. The table below covers the most common equipment found in Australian workshops and maintenance facilities. Machine Type Typical MT Size Notes Benchtop / hobby drill press (up to 13mm chuck) MT1 or MT2 Most 13mm benchtop machines are MT2. Some compact machines are MT1. Check the manual or measure (see below). Floor-standing drill press (up to 16mm chuck) MT2 or MT3 MT3 is standard on quality floor-standing machines. Budget/imported machines often MT2. Industrial/radial arm drill press MT4 or MT5 Larger spindle bore for heavy-duty drilling. MT4 most common in 40mm+ capacity machines. Lathe tailstock — small (up to 200mm swing) MT1 or MT2 Most 9" and 10" lathes (Hafco AL-250, Hare and Forbes similar) use MT2 tailstock. Lathe tailstock — medium (200-400mm swing) MT2 or MT3 MT3 common on 300-400mm swing machines. MT2 on many Chinese-made lathes at the 300mm size. Lathe tailstock — large (400-600mm swing) MT4 or MT5 Heavy-duty production lathes. MT4 most common at this size. Lathe headstock (self-holding spindle) MT3 to MT6 Many smaller lathes have an MT headstock for centres and faceplates. Large industrial lathes use MT5 or MT6 headstock. Knee-type milling machine MT3 or MT4 Some older knee mills use MT spindle (not ISO or CAT). Bridgeport uses R8, not Morse. Small boring machine / jig borer MT3 to MT5 Varies significantly by make and age. Woodworking lathe headstock / tailstock MT1, MT2 or MT3 Many woodworking lathes use MT2 at both ends. Some larger bowl-turning lathes use MT3 tailstock. If your machine is not on this list: check the manual, look for a data plate on the machine, or measure the large end diameter of the female socket as described in the next section. A set of Morse taper gauges will identify the size in seconds; a digital calliper or telescoping gauge plus micrometer will do it just as well. How to Identify Your Morse Taper Size If you have a machine and don't know what Morse taper size it takes, the fastest method is to measure the large end diameter of the female socket at the face (gage line) of the spindle or tailstock quill. This is the only dimension that's easily accessible when the taper is inside a machine. What you need A telescoping gauge and an outside micrometer, or a digital calliper if the bore geometry allows it. On most lathe tailstocks and drill press spindles, a set of outside jaw calipers will reach the bore opening directly. Step-by-step identification Retract the tailstock quill or raise the drill press spindle fully, so the opening is as exposed as possible. Measure the bore diameter at the face — the outermost ring of the opening. This is the large end of the female taper. Compare your measurement to the large end diameters in the table above. For example, if your measurement is 17.7-17.9mm, you have an MT2. If it measures 23.7-24.0mm, you have MT3. Test with a known tool once you have a candidate size. An MT2 drill shank should drop cleanly into an MT2 socket and seat firmly without forcing. If it drops straight through, it is too small. If it won't enter more than a few millimetres, it is too large. On the male shank: if you have a tool with a Morse taper shank and want to identify its size, you can measure the large end diameter at the gage line (the step or undercut just behind the main taper). Alternatively, hold it against a known MT2 or MT3 shank — visual comparison is often sufficient for neighbouring sizes. Common measurement errors: measuring mid-taper rather than at the face; measuring a worn or damaged bore that has been enlarged; confusing a Jacobs taper bore (often present on older drill press quills alongside a Morse taper spindle) with the Morse taper itself. The Jacobs taper is steeper and shorter — if your measurement doesn't match any Morse taper size, check whether you are looking at a Jacobs taper instead. How to Fit a Morse Taper Tool Correctly A Morse taper that is not properly cleaned and seated will vibrate, chatter, and potentially drop the tool into the workpiece. Correct fitting takes 30 seconds. Clean the female socket. Wipe the bore with a clean rag or lint-free cloth. Remove any swarf, oil residue, moisture, or old debris. Even a thin film of oil on both surfaces reduces holding force significantly — clean and dry gives the best friction. Clean the male shank. Wipe the shank with the same clean cloth. Inspect for nicks, raised burrs, or rust spots. A burr on the taper surface will prevent full seating; stone it off with a small oilstone before fitting. Orient the tang. The tang must align with the drift slot in the socket before you push the shank in. On most drill press spindles, the drift slot runs front-to-back (perpendicular to the column). On lathe tailstocks, it is usually on the left side facing the operator. Insert firmly. Push the shank in with a sharp, firm thrust — heel of the hand or a soft mallet. You should feel it seat with a slight thud. A properly seated Morse taper will resist a moderate rotational force by hand. Check seating. With the machine off, try to rotate the tool in the socket with firm hand pressure. If it rotates easily, remove and repeat: clean, check for burrs, and reseat. If it seats firmly but pulls out under light axial load, the taper surfaces may be worn or the bore may be slightly oversize — see the troubleshooting notes in the removal section below. How to Remove a Morse Taper — The Drift Method The correct tool for removing a Morse taper is a drift — a flat, tapered wedge of steel that fits the drift slot cast through the socket. Do not use a screwdriver, a chisel, or an Allen key in the drift slot. These will damage the tang or spread the slot, making future drift use unreliable. Standard drift removal — step by step Position the drift in the drift slot in the socket — the rectangular opening you can see in the side or back of the quill. The drift tapers from thick to thin; the thicker end faces away from the direction of travel you intend. Strike the drift with a hammer — a single firm tap is usually enough. The drift pushes down against the tang of the tool, driving the taper out axially. Catch the tool. Have a hand ready below the chuck or tool, particularly on a drill press where the spindle is overhead. Once the taper breaks free, the tool drops. What to do when the taper is stuck A stuck taper is one of the most common workshop problems. The usual cause is a taper that has been seated very hard — either by vibration accumulating during drilling, by the tool being struck with excessive force during fitting, or by rust or corrosion bonding the surfaces. Standard drift removal still works in most cases; you may need several firm strikes rather than one. Vibration method: If the drift is not shifting it, try a sharp lateral rap on the quill body (not on the taper shank itself) with a soft-face mallet. The vibration breaks the surface adhesion between the tapers. Several sharp strikes followed immediately by a drift tap often releases a taper that seemed immovable. Heat differential: Warming the outer socket — with a heat gun on low, not a torch — causes it to expand slightly before the inner shank does. Even a 50-80 degree Celsius temperature differential is often enough to break the lock. Apply heat around the socket body for 30-60 seconds, then attempt drift removal immediately. Do not use this method on high-speed steel tooling that may be sensitive to heat, or if there are rubber seals or plastic components nearby. Penetrating oil: If corrosion is a factor, apply penetrating oil (CRC, WD-40 equivalent) to the drift slot and allow it to wick in overnight. Strike the following day. What not to do: Do not apply the drill press quill feed lever as a prying tool against the shank. Do not wedge screwdrivers into the gap between taper and socket. Both damage the socket bore and may score the taper shank, making future seating unreliable. Taper not holding — diagnosis If a Morse taper shank will not hold in service — spinning or pulling out during use — the cause is nearly always one of the following: Contamination: Oil, coolant, or swarf on the mating surfaces. The fix is cleaning, not overtightening. Worn or damaged socket: Scoring on the female bore from past misuse. Inspect with a light and a clean cloth. Minor scoring may be polished out; severe damage requires a reamer to restore geometry. Wrong size: An MT2 shank in an MT3 socket will appear to seat but has only line contact rather than full surface contact. It will not hold under load. Use the correct size or a reducing sleeve. Soft or damaged shank: Reground drill shanks, repaired shanks, or cheap import tooling occasionally has the taper angle ground incorrectly. Compare against a known good shank from the same nominal size. Morse Taper Sleeve Adapters and Socket Reducers Morse taper sleeves (also called adapter sleeves or socket reducers) allow a tool with one MT size to be used in a machine with a different MT socket. There are two types. Reducing sleeves (most common) A reducing sleeve has a larger female socket at one end and a smaller male taper at the other. For example, an MT3-to-MT2 reducing sleeve fits a machine with an MT3 socket and accepts an MT2 shank tool. This is the configuration you will almost always need — when you buy drill bits with MT2 shanks for a lathe that takes MT3 in the tailstock, you need a reducing sleeve between them. Common reducing sleeve combinations in Australian workshops: MT2 to MT1: Accommodates MT1-shank tools in an MT2 machine. Common for small reamers and centres on benchtop drill presses. MT3 to MT2: The most commonly used combination — MT2 tools (including most drill chuck arbors and smaller drill bits) in an MT3 machine. Standard for medium floor drill presses and lathe tailstocks. MT4 to MT3: Large industrial drill presses and lathe tailstocks using MT3 tooling. MT4 to MT2: Two-step reduction in a single sleeve. Less rigid than stacking two separate sleeves. Extension sleeves An extension sleeve (also called a socket adapter) fits a smaller male taper into a larger machine socket. These are less common in standard workshop practice but are used when a machine's spindle is a large MT size and you need to use large-format accessories — for example, mounting an MT5 boring head into an MT4 tailstock with an MT4-to-MT5 extension is occasionally specified in retrofitting older equipment. Stacking sleeves Multiple reducing sleeves can be stacked in sequence — MT4 machine to MT3-to-MT2 sleeve to MT2-to-MT1 sleeve to MT1 tool. This works but adds length to the setup, which increases overhang and potential for vibration. Use the shortest sleeve path possible for a given application. Selecting a sleeve When buying sleeves, ensure the product is machined to DIN 228 / ISO 296 dimensions. Inexpensive sleeves with incorrect taper angles will seat loosely at one or both ends, causing the tool to run out and creating dangerous conditions. Check that the drift slots on any sleeve you buy are accessible when the sleeve is in the machine — some designs require sequential removal (sleeve must come out with the tool, then both are ejected from the machine socket). Morse Taper vs Jacobs Taper vs R8 — What's the Difference? Three taper standards appear frequently in Australian workshop equipment. Understanding the difference prevents the common mistake of ordering the wrong arbor or adapter. Feature Morse Taper (MT) Jacobs Taper (JT) R8 Taper Primary use Lathe tailstocks, drill press spindles, general toolholding Mounting drill chucks to arbors Milling machine spindles (Bridgeport-type) Self-holding? Yes Yes No — requires drawbar Sizes MT0 to MT7 JT0 to JT33 (most common JT1, JT2, JT3, JT6) One size only (3.500" per foot taper) Included angle Approx 2.9 deg (varies slightly by size) Approx 2.33 deg (varies by size) 16.51 deg Torque transmission Friction (tang for ejection only) Friction (no tang) Friction + drawbar axial clamping Where you see it Drill shanks, lathe centres, reamers, arbors Drill chuck mounting interface Bridgeport and compatible mill spindles Standard DIN 228 / ISO 296 JT (Jacobs proprietary, widely adopted) Bridgeport specification Morse Taper vs Jacobs Taper These two tapers are often confused because they appear on the same component — a drill chuck arbor. The arbor has a Morse taper on the machine end (male shank that seats in the lathe tailstock or drill press spindle) and a Jacobs taper on the chuck end (male taper that seats in the back of the chuck). Neither is interchangeable with the other. When you buy a drill chuck arbor, you need to specify both: the MT size for the machine and the JT size for the chuck. Common drill chuck arbor specifications in Australian workshops: MT2 x JT2 — for machines with MT2 spindles and chucks with JT2 bore (most common benchtop configuration) MT3 x JT3 — for machines with MT3 spindles and larger chucks MT2 x JT33 — for machines with MT2 spindles and smaller precision chucks Morse Taper vs R8 R8 appears exclusively on Bridgeport-type knee mills and their clones. It is a steeper taper than Morse — steep enough that it cannot self-hold and requires a drawbar (a threaded rod running through the spindle from top to bottom) to keep the toolholder from pulling out under lateral milling forces. If your milling machine has a drawbar poking out the top of the spindle, it almost certainly uses R8. Morse taper tooling will not fit an R8 spindle directly. You cannot use a reducing sleeve to make MT tooling work in an R8 machine — the geometry and clamping method are fundamentally different. Morse Taper Drill Bits — What You Need to Know Most workshop drill bits up to 13mm diameter are straight-shank — they grip in a three-jaw chuck. Above a certain diameter, the shank transitions to a Morse taper. The transition point varies by manufacturer and country of origin, but in Australia the most common convention is: Up to 13mm: Straight shank (fits in a 13mm chuck) 14mm to 23mm: MT2 taper shank (too large for a standard chuck jaw) 24mm to 31mm: MT3 taper shank 32mm and above: MT4 taper shank These are general conventions — always check the specification for a given drill series. Sutton Tools, as the dominant Australian manufacturer of industrial drill bits, follows this convention for their HSS and cobalt drill ranges. When you drill a 20mm hole on a drill press that takes MT3, you will need an MT3-to-MT2 reducing sleeve to use a standard MT2-shank 20mm drill. Morse taper shank reamers Machine reamers — used to bring bored or drilled holes to precise diameter — are almost universally supplied with Morse taper shanks. This is one of the oldest applications of the standard; Morse taper reamers predate Morse taper drill bits in industrial practice. Reamer shank size follows the same diameter conventions as drill bits: small reamers on MT1 or MT2, larger reamers on MT3 and above. Tapered shank drill bits on a lathe tailstock The lathe tailstock is a natural home for Morse taper drilling. Fit the drill directly into the tailstock quill (with a reducing sleeve if necessary), lock the quill, and advance the tailstock by hand or power feed. This produces accurate, concentric holes because the drill runs true to the lathe centreline. Centre drills, spot drills, and combination drill-countersinks for lathe work are all commonly supplied with MT1 or MT2 shanks. When using a drill chuck in the lathe tailstock, the same MT + JT arbor arrangement described above applies. Many machinists keep one chuck arbor permanently set up for each tailstock they use — it saves re-seating the chuck for every job. Buying Morse Taper Tooling — What to Look For Not all Morse taper tooling is made equal. The taper angle and surface finish tolerances matter far more than they do for straight-shank tooling, because any deviation in the taper geometry directly affects seating, runout, and holding force. Here is what to check before you buy. Taper accuracy grade Industrial standard Morse taper tooling is graded to AT3 (medium precision) or AT4 (high precision) under ISO 1947. Consumer-grade import tooling is often ungraded and may be ground to a wider tolerance. For general workshop drilling and turning, AT3 is entirely adequate. For reaming, precision boring, and close-tolerance lathe work, AT4 is worth the premium. If a supplier cannot tell you the accuracy grade of a sleeve or arbor, treat it as ungraded. Material and hardness Morse taper shanks on drill bits and reamers should be hardened high-speed steel (HSS) or alloy steel. The taper surfaces need to be hard enough to resist fretting and wear — a soft shank will gradually lose geometry after repeated seating and removal cycles. Reducing sleeves and arbors are typically made from medium-carbon steel, case-hardened on the taper surfaces. Cheap sleeves with soft taper surfaces will wear rapidly in a production environment. Drift slot position and accessibility For sleeves, check that the drift slot is accessible when the sleeve is fitted in your specific machine. Some machine designs have limited access to the quill drift slot, and longer sleeves may cover it. Fit a sleeve dry before buying a full set — or at minimum, confirm the slot position against your machine's documentation. Surface finish on the taper The taper surfaces should be smooth and clean, with no visible grinding marks, scratches, or machining chatter. Run your fingernail lightly along the taper body — it should feel glassy. Any roughness will increase running wear and reduce holding force. Brands in the Australian market Sutton Tools (Melbourne) remains the gold standard for HSS and cobalt drill bits in the Australian industrial market. Their MT-shank drill ranges — including the Series 260 jobber and the Viper cobalt range — are consistently manufactured to correct taper geometry and are carried by most industrial suppliers. For reducing sleeves and arbors, ToolmEx, Vertex, and Bison (Poland) are well-regarded. Generic import sleeves are adequate for low-duty applications; avoid them for production reaming or precision work. AIMS Industrial stocks a range of Morse taper drill bits and accessories for Australian trade and industrial customers. Browse drill bits at AIMS Industrial, or contact our team if you need help specifying the right combination of shank, sleeve, and chuck for your machine. Morse Taper in Practice — Common Australian Workshop Configurations The following configurations cover the vast majority of Morse taper situations you will encounter in Australian trade and maintenance workshops. Use these as a quick-start reference when setting up tooling for a job. Small benchtop drill press (MT2 spindle) This is the most common configuration in home workshops, light fabrication shops, and maintenance departments running a small standalone drilling station. Direct drilling (14-23mm): MT2-shank drill bit — fits directly in the spindle with no sleeve. Chuck work (up to 13mm): MT2 x JT2 or MT2 x JT33 drill chuck arbor. Keep one permanently fitted to your most-used chuck. Reamers: MT1 or MT2 shank depending on reamer diameter — use an MT2-to-MT1 reducing sleeve if needed. Centre drills: MT2-shank combination drill/countersink for lathe work, or a straight-shank centre drill in the MT2 chuck. Floor-standing drill press (MT3 spindle) Quality floor-standing machines — the sort found in engineering shops, TAFE workshops, and well-equipped maintenance facilities — almost always run MT3. Large diameter drilling (24-31mm): MT3-shank drill bit fits directly. No sleeve needed. Standard drilling (14-23mm): MT2-shank drill bit + MT3-to-MT2 reducing sleeve. Keep a sleeve permanently fitted to your most-used MT2 drill. Chuck work: MT3 x JT3 arbor and a quality 16mm or 20mm keyless chuck. This is the most versatile setup for mixed drilling work. Annular cutters: Many annular cutter systems (Hougen, BDS, Karnasch) use a Weldon shank rather than a Morse taper, but MT-shank versions exist and seat directly in MT3 spindles without an adapter. Medium lathe tailstock (MT2 or MT3) Australian workshop lathes in the 250-350mm swing range are split between MT2 (most budget Chinese imports) and MT3 (quality machines from Taiwan, European, or older Australian/UK manufacture). The configuration differences are significant enough to check your machine before buying tooling. Live centres: Always specify the shank size for your tailstock. MT2 live centres are not interchangeable with MT3 without a sleeve, and running a live centre via a sleeve adds length (reduces maximum component length between centres) and can introduce slight runout. Dead centres: Same rules as live centres. Keep a matched set — tailstock dead centre, headstock dead centre — labelled with their MT size. Drill chuck in tailstock: MT2 x JT2 arbor for MT2 tailstocks; MT3 x JT3 for MT3. Many machinists use a Jacobs 34 or 36 heavy-duty chuck on a JT3 arbor for hard drilling in the tailstock — the larger chuck bore handles the larger shanks of bigger drills. Direct MT drilling in tailstock: Lock the quill at a comfortable extension, advance the tailstock by handwheel. This is faster and more rigid than drilling through a chuck. For repeatable depth, mark the quill with a felt tip or use the quill depth stop. Tooling you should have on the shelf For any workshop that uses a lathe and a drill press, the following Morse taper items are the minimum useful stock: One MT3-to-MT2 reducing sleeve (covers most cross-size situations) One MT2 drift and one MT3 drift (never be without the right size) One MT2 x JT2 drill chuck arbor (benchtop drill press, lathe tailstock) One MT3 x JT3 drill chuck arbor (floor drill press, larger lathe tailstock) One MT2 live centre and one MT3 live centre (long-term investment — buy quality) One MT2 dead centre set (60-degree and bull-nose) for the headstock If you're unsure what's already in your workshop, do a taper audit: identify the MT size of every machine's spindle and tailstock, label each with a paint marker or tag, and cross-check your tooling against the list. You'll probably find you have duplicate sizes you don't need and gaps you didn't know about. Contact AIMS Industrial if you need help pulling together the right combination. Cleaning, Care and Storage The condition of the mating taper surfaces is the single biggest factor in holding force. A clean, lightly polished taper in a clean socket will hold more reliably than a heavier, newer taper in a contaminated socket. Routine cleaning Before fitting any Morse taper tool, wipe both the shank and the socket with a clean, dry cloth. This takes 10 seconds and eliminates the most common cause of slip and chatter. Do not use lubricating oil on the mating surfaces — oil reduces friction and therefore reduces holding force. The surfaces should be clean and dry. For the female socket, a purpose-made Morse taper cleaning spindle — a wooden or plastic mandrel wrapped with lint-free cloth — inserted, rotated, and withdrawn will clean the bore cleanly. A rag draped over a finger also works on accessible sockets. Preventing rust and corrosion After a long period of non-use, apply a very light film of CRC 5-56, WD-40, or light machine oil to both the shank and the socket, then wipe it off before use. The purpose is corrosion prevention, not lubrication — the surfaces must be dry when you fit the taper. Taper shanks stored in a damp environment (common in unheated garages and sheds across southern Australia during winter) are particularly prone to rust-spotting. A light coating of anti-rust oil on stored shanks, combined with wrapping in oiled paper or storing in a plastic sleeve, prevents this. Even minor surface rust on the taper body should be polished off with fine emery paper before the tool is used — raised rust pitting prevents full contact between the mating surfaces. Inspecting for wear Over many years of use, the female socket of a heavily used machine may wear slightly oversize at the entrance — the area subject to the most contact during tool insertion and removal. Inspect by fitting a known-good, clean taper shank and checking for visible contact pattern (apply Prussian blue or engineer's marking paste to the shank, insert, rotate slightly, withdraw, and observe where the marking transferred). Full contact along the length of the taper is the goal. A contact pattern that only shows at the front or only at the back indicates the socket geometry has shifted. Resizing with a Morse taper reamer is the correct remedy; replacement of the quill or spindle is the last resort. Frequently Asked Questions What does the number after MT mean — what is MT2 vs MT3? The number indicates the size of the taper. Higher numbers mean larger diameter and longer length. MT2 has a large-end diameter of 17.78mm; MT3 is 23.83mm. The two cannot be used interchangeably without a reducing sleeve. MT2 is the most common size for benchtop machines; MT3 is standard on quality floor-standing drill presses and medium lathes. A full dimension table appears above. Why is it called a Morse taper? The taper is named after Stephen A. Morse (1838-1921), a drill manufacturer from New Bedford, Massachusetts, who developed the design around 1864. Morse made twist drills and needed a reliable way to mount them in machine spindles. His design was adopted as a de facto standard across the American and then global machine tool industry over the following decades. What angle is a Morse taper? The included angle is approximately 2.86 to 3.01 degrees, depending on the specific MT size (each size has a slightly different taper ratio to maintain consistent self-holding characteristics as diameter increases). The angle from the centreline is approximately 1.43 to 1.51 degrees. The taper is usually expressed as a ratio — MT2, for example, is 1:20.02 (one unit of diameter change for every 20.02 units of length). These shallow angles keep the taper below the friction angle of steel-on-steel, which is what makes it self-holding. Is a Morse taper the same as a Jacobs taper? No. Both are self-holding tapers, but they serve different purposes and are not interchangeable. Morse tapers connect tools (drill shanks, centres, reamers) to machine spindles. Jacobs tapers connect drill chucks to arbors. A drill chuck arbor typically has a Morse taper on one end (machine side) and a Jacobs taper on the other (chuck side). Jacobs taper angles are slightly different from Morse taper angles, and the two taper series use completely different size numbering. How do I know what Morse taper my lathe takes? Check the manual or data plate on the machine. If neither is available, measure the large end diameter of the female socket at the face of the tailstock quill (with the quill fully retracted). Compare your measurement to the large end diameter column in the table above. For example, 17.7-17.9mm is MT2; 23.7-24.0mm is MT3. You can also test with a known tool of each size — the correct size drops smoothly into the socket and seats firmly without forcing. Can I use a Morse taper drill in a Jacobs chuck? Not directly — the Morse taper shank is too large for a standard drill chuck to grip. For large-diameter drills (typically 14mm and above) with MT shanks, you fit the drill directly into the machine spindle or tailstock (with a reducing sleeve if the socket is larger than the shank). If you want to use a Morse taper shank drill in a chuck, you would need a chuck with an internal Morse taper bore — these exist but are specialist items. What is a Morse taper drift and where does it go? A drift is a flat, tapered wedge of steel used to eject tools from a Morse taper socket. Every Morse taper socket has a rectangular cross-slot through it — the drift slot — positioned so that a drift inserted into it contacts the flat tang at the end of the taper shank. Tapping the drift with a hammer pushes the tang, which drives the taper shank out axially. The drift slot size and position correspond to the MT number. MT2 drifts are not the same as MT3 drifts — use the correct size. How do I remove a Morse taper that is stuck? First, use a proper drift (see above) and strike it firmly. Most stuck tapers respond to a harder strike than initially applied. If that fails: (1) give the quill body several sharp lateral raps with a soft-face mallet to induce vibration, which breaks surface adhesion, then try the drift again; (2) apply penetrating oil into the drift slot and allow it to wick overnight; (3) apply gentle heat (heat gun on low) around the socket body for 60 seconds to expand it slightly before attempting drift ejection. Do not pry at the taper interface with screwdrivers or chisels — this damages both the shank and the socket. What is the difference between a Morse taper and an R8 taper? A Morse taper is self-holding — its shallow angle (approximately 3 degrees included) locks the tool in place through friction without a drawbar. R8 is a much steeper taper (16.51 degrees included) used exclusively in Bridgeport-type knee milling machines. R8 is self-releasing — the steep angle means it would pull out under milling forces without a drawbar clamping it from above. The two are not interchangeable. Morse taper tooling does not fit R8 spindles and vice versa. Do Morse taper sleeves affect accuracy? A sleeve machined to DIN 228 / ISO 296 standards will add minimal runout — typically less than 0.01mm with quality tooling. Cheap sleeves with inaccurate taper geometry can add 0.05mm or more of runout, which is significant for reaming, fine drilling, and turning operations. For precision work, buy sleeves from reputable manufacturers and inspect the contact pattern before use (Prussian blue test on both mating surfaces). Stacking multiple sleeves compounds any runout error — use a single sleeve where possible. What size Morse taper do Sutton drill bits use? Sutton Tools follows the standard Australian convention: straight shank up to 13mm, MT2 from 14mm to approximately 23mm, MT3 from 24mm to 31mm, and MT4 from 32mm upward. Always confirm the shank specification in the Sutton product listing for a given series, as the cobalt and carbide ranges may differ slightly from the HSS range in how the shank transition point is specified. Can I use a Morse taper without the tang? Yes. The tang's only function is to contact the drift during removal — it does not transmit torque or contribute to holding force. Drill shanks that have had their tangs twisted or broken off can still be used in sockets designed for them, called "tang-free" or "Tang-Eject" sockets (a Morse sleeve or arbor that allows push-out with the drift even without the tang present). In a standard socket, a tang-free shank can still be seated and will hold normally — the challenge is removal, which requires a different ejection method (usually a special puller or a small internal drift). Are Morse tapers the same worldwide? Yes. DIN 228 Part 1 (Germany) and ISO 296 are the international standards for Morse taper dimensions, and they define identical dimensions. A Sutton MT2 drill bit made in Australia will fit an MT2 socket on a machine made in Germany, Japan, the UK, or the United States. The Morse taper was de facto standardised globally before the formal DIN/ISO standards were written — the standards simply codified existing practice. One exception: very old US-made machinery manufactured before approximately 1880-1890 may have pre-standard Morse dimensions that differ slightly from the modern specification. This is vanishingly rare in Australian workshops. Pair this guide with our Socket Size Chart for matching socket to bolt head across systems. Browse long drill bits at AIMS Industrial for application support and stock confirmation. For jobber drill bits, see our jobber drill bits range stocked across Australia. People Also Ask — Morse Tapers Q: What is the purpose of a Morse Taper on a drill bit? The Morse Taper on a drill bit allows it to mount directly into a lathe headstock, drill press spindle, or milling machine quill without a chuck. The tapered shank self-centres automatically as it seats into the matching socket, and the self-holding taper angle grips the tool under cutting load without any separate locking mechanism. Larger diameter drills — typically above 13mm — use Morse Taper shanks because they can transmit more torque than a parallel shank held in chuck jaws. Taper-shank drills are more rigid in the spindle and run with less runout than chuck-mounted tooling. Q: How do you remove a Morse Taper tool from a drill press? A drift key — a flat tapered steel bar — is the standard tool for removing a Morse Taper. The drift is inserted into the slot on the side of the quill or sleeve and tapped with a hammer, breaking the taper’s self-holding grip by applying lateral force rather than axial pull. Never strike the drill bit itself or try to lever it out, as this can damage both the taper socket and the shank. Some drill presses have a built-in ejection mechanism that operates when the quill is retracted to its uppermost position. If a taper has been in service for a long time and is seized, penetrating oil applied to the joint followed by light tapping of the drift usually frees it. Q: Can you use a Morse Taper 2 tool in a Morse Taper 3 socket? Yes, using an adapter sleeve. A reducing sleeve converts a larger taper socket to accept a smaller taper shank — for example, an MT2-to-MT3 sleeve allows an MT2 tool to run in an MT3 machine spindle. The sleeve seats in the machine socket and the tool’s taper seats into the sleeve. Adapter sleeves maintain the self-holding properties of both tapers when correctly fitted. Extending the other direction — fitting a larger taper tool into a smaller socket — is not possible with a sleeve; a larger-capacity machine spindle is required. Q: What does 'self-holding taper' mean for a Morse Taper? A self-holding taper has a shallow taper angle — in the range of 1.5° to 3° — that creates enough friction between the mating surfaces to hold the tool in place under normal cutting loads without any locking device. When driven in firmly, the taper grips itself and will not pull out during cutting operations. The trade-off is that a drift key is needed to break the friction grip when removing the tool. Self-holding tapers contrast with steep-taper machine tool connections (such as CAT and BT taper spindles) which require a draw bar to maintain engagement. Q: Which Morse Taper size is most common for workshop drills? MT2 is the most common Morse Taper for general workshop use, fitting taper-shank drill bits from approximately 14mm up to 23mm diameter. MT3 is standard on larger drill presses and lathes and accepts larger drills. MT1 appears on smaller taper-shank drills and some lathe centres used for lighter work. MT4 and above are found on large industrial machines. The specific Morse Taper number required by a machine is listed in its technical specification — always match the taper number to the machine spindle to ensure the self-holding fit and correct taper geometry.
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Drill Bit Size Chart: Metric, Imperial & Fractional
Drill Bit Selector — Most-Asked Sizes This page is a working selector tool — not just a reference. Use it to get the right drill bit into your hand in one click. The 10 most-asked drill sizes at AIMS are below. For less common sizes, scroll to the full conversion chart further down. How to use: 1. Find your drill size 2. Click Buy drill 3. Confirm material match using the "By Material" section below 3 mm HSS jobber drill Buy drill → 4 mm HSS jobber drill Buy drill → 5 mm HSS jobber drill Buy drill → 6 mm HSS jobber drill Buy drill → 6.5 mm HSS jobber drill Buy drill → 8 mm HSS jobber drill Buy drill → 10 mm HSS jobber drill Buy drill → 12 mm HSS jobber drill Buy drill → 13 mm HSS jobber drill Buy drill → 16 mm HSS jobber drill Buy drill → Default recommendation: Sutton D101 Silver Bullet HSS jobber drill — the workshop standard for occasional drilling in mild steel, aluminium, plastics and timber. For production steel work switch to D102 Blue Bullet (steam oxide finish). For stainless steel or hardened material, use D108 or D109 cobalt drill bits. For concrete and masonry, use D600 / D601 TCT masonry drill bits (linked in the Anchor Bolt sections below). Need help? Call us on (02) 9773 0122. Jump to: Quick Reference Full Conversion Chart By Material Anchor Bolt Sizes Related Selectors Imperial Drill Bit Sizes in Millimetres — Quick Reference The fastest way to convert a fractional or imperial drill bit size to millimetres is the constant 25.4 mm per inch. So 1/8" = 3.175 mm, 5/32" = 3.969 mm, 3/16" = 4.763 mm, 7/32" = 5.556 mm, 1/4" = 6.350 mm, 5/16" = 7.938 mm, 3/8" = 9.525 mm and 15/64" = 5.953 mm. The full metric, imperial and fractional cross-reference chart sits in the body below. What size is a 1/8" drill bit in mm? 1/8" equals 3.175 mm exactly (1 ÷ 8 × 25.4). The closest standard metric drill bit is 3.2 mm. What size is a 3/16" drill bit in mm? 3/16" equals 4.763 mm (3 ÷ 16 × 25.4). The closest standard metric drill bits are 4.8 mm or 5.0 mm. What is the standard mm size of a 5/32" drill bit? 5/32" equals 3.969 mm (5 ÷ 32 × 25.4). The closest standard metric drill bit is 4.0 mm. Use this drill bit size chart to cross-reference metric (mm), imperial (fractional and decimal inches), and gauge sizes — including number and letter — in a single reference table. Whether you're sizing a pilot hole for a screw or bolt, converting between measurement systems, or identifying an unmarked bit, find your size below and read across the row for the equivalent. Quick conversion — most-searched sizes Imperial to metric: 1/8" = 3.175mm · 5/32" = 3.97mm · 3/16" = 4.76mm · 7/32" = 5.56mm · 1/4" = 6.35mm · 5/16" = 7.94mm · 3/8" = 9.525mm · 7/16" = 11.11mm · 1/2" = 12.7mm · 9/16" = 14.29mm · 5/8" = 15.88mm · 3/4" = 19.05mm · 1" = 25.4mm Metric to imperial: 3mm ≈ 1/8" · 4mm ≈ 5/32" · 5mm ≈ 13/64" · 6mm ≈ 15/64" · 8mm ≈ 5/16" · 10mm ≈ 25/64" · 12mm ≈ 15/32" Full metric / fractional / number / letter cross-reference table below. This guide is part of AIMS Industrial's curated Engineering Reference Charts library — 78 reference articles across fasteners, threading, bearings, lubrication and safety standards. Drill Bit Size Chart — Quick Reference Quick conversion between the most common metric (mm) and imperial (fractional inch) drill bit sizes. Full cross-reference table with number and letter gauge sizes is below. Metric (mm) Fractional Inch Decimal Inch 3.0 mm 1/8" 0.1181 4.0 mm 5/32" 0.1575 5.0 mm 13/64" 0.1969 6.0 mm 15/64" 0.2362 8.0 mm 5/16" 0.3150 10.0 mm 25/64" 0.3937 12.0 mm 15/32" 0.4724 16.0 mm 5/8" 0.6299 20.0 mm 25/32" 0.7874 25.4 mm 1" 1.0000 How to Use This Chart The table covers drill bit sizes from 0.010mm to 25.4mm (1 inch). Find your required hole size in the metric or imperial column and read across to identify the equivalent gauge number, letter, fractional, or decimal size. A few things to keep in mind. Not all metric drill bits have imperial equivalents and vice versa. Some metric values are close enough to share the same imperial counterpart. Values are rounded to the nearest thousandth millimetre or ten-thousandth decimal inch. Need help finding your size? Call AIMS on (02) 9773 0122 — the team can confirm stock and pick the right drill type for your material. Or browse all jobber drill bits. Gauge Sizing Metric / SI Imperial / US Number / Letter Size Millimeters Fractional Inches Fractional Inches (Reduced) Decimal Inches --- 0.010 --- --- 0.0004 104 0.080 --- --- 0.0031 103 0.090 --- --- 0.0035 102 --- --- --- 0.0039 --- 0.100 --- --- 0.0039 101 0.110 --- --- 0.0043 100 0.120 --- --- 0.0047 99 0.130 --- --- 0.0051 98 0.140 --- --- 0.0055 97 0.150 --- --- 0.0059 96 0.160 --- --- 0.0063 95 0.170 --- --- 0.0067 94 0.180 --- --- 0.0071 93 0.190 --- --- 0.0075 --- 0.198 1/128 --- 0.0078 92 0.201 --- --- 0.0079 91 0.210 --- --- 0.0083 90 0.220 --- --- 0.0087 89 0.230 --- --- 0.0091 88 0.240 --- --- 0.0095 --- 0.250 --- --- 0.0098 87 0.254 --- --- 0.0100 --- 0.260 --- --- 0.0102 86 0.270 --- --- 0.0105 85 0.280 --- --- 0.0110 84 0.290 --- --- 0.0115 --- 0.300 --- --- 0.0118 83 0.305 --- --- 0.0120 82 0.318 --- --- 0.0125 81 0.330 --- --- 0.0130 80 0.343 --- --- 0.0135 79 0.368 --- --- 0.0145 --- 0.397 1/64 --- 0.0156 78 0.406 --- --- 0.0160 77 0.457 --- --- 0.0180 --- 0.500 --- --- 0.0197 76 0.508 --- --- 0.0200 75 0.533 --- --- 0.0210 74 0.572 --- --- 0.0225 73 0.610 --- --- 0.0240 72 0.635 --- --- 0.0250 71 0.660 --- --- 0.0260 70 0.710 --- --- 0.0280 69 0.742 --- --- 0.0292 --- 0.750 --- --- 0.0295 68 0.787 --- --- 0.0310 --- 0.794 2/64 1/32 0.0312 67 0.813 --- --- 0.0320 66 0.838 --- --- 0.0330 65 0.889 --- --- 0.0350 64 0.914 --- --- 0.0360 63 0.940 --- --- 0.0370 62 0.965 --- --- 0.0380 61 0.991 --- --- 0.0390 --- 1.000 --- --- 0.0394 60 1.016 --- --- 0.0400 59 1.041 --- --- 0.0410 58 1.067 --- --- 0.0420 57 1.092 --- --- 0.0430 56 1.181 --- --- 0.0465 --- 1.191 3/64 --- 0.0469 --- 1.250 --- --- 0.0492 55 1.321 --- --- 0.0520 54 1.397 --- --- 0.0550 --- 1.500 --- --- 0.0591 53 1.511 --- --- 0.0595 --- 1.588 4/64 1/16 0.0625 52 1.613 --- --- 0.0635 51 1.702 --- --- 0.0670 --- 1.750 --- --- 0.0689 50 1.778 --- --- 0.0700 --- 1.800 --- --- 0.0709 --- 1.850 --- --- 0.0728 49 1.854 --- --- 0.0730 48 1.930 --- --- 0.0760 --- 1.984 5/64 --- 0.0781 47 1.994 --- --- 0.0785 --- 2.000 --- --- 0.0787 46 2.057 --- --- 0.0810 45 2.083 --- --- 0.0820 44 2.184 --- --- 0.0860 --- 2.250 --- --- 0.0886 43 2.261 --- --- 0.0890 42 2.375 --- --- 0.0935 --- 2.381 6/64 3/32 0.0938 41 2.438 --- --- 0.0960 --- 2.450 --- --- 0.0965 40 2.489 --- --- 0.0980 --- 2.500 --- --- 0.0984 39 2.527 --- --- 0.0995 38 2.578 --- --- 0.1015 37 2.642 --- --- 0.1040 36 2.705 --- --- 0.1065 --- 2.750 --- --- 0.1083 --- 2.778 7/64 --- 0.1094 35 2.794 --- --- 0.1100 34 2.819 --- --- 0.1110 33 2.870 --- --- 0.1130 32 2.946 --- --- 0.1160 --- 3.000 --- --- 0.1181 31 3.048 --- --- 0.1200 --- 3.175 8/64 1/8 0.1250 --- 3.250 --- --- 0.1280 30 3.264 --- --- 0.1285 29 3.454 --- --- 0.1360 --- 3.500 --- --- 0.1378 28 3.569 --- --- 0.1405 --- 3.572 9/64 --- 0.1406 27 3.658 --- --- 0.1440 26 3.734 --- --- 0.1470 --- 3.750 --- --- 0.1476 25 3.797 --- --- 0.1495 24 3.861 --- --- 0.1520 23 3.912 --- --- 0.1540 --- 3.969 10/64 5/32 0.1562 22 3.988 --- --- 0.1570 --- 4.000 --- --- 0.1575 21 4.039 --- --- 0.1590 20 4.089 --- --- 0.1610 19 4.216 --- --- 0.1660 --- 4.250 --- --- 0.1673 18 4.305 --- --- 0.1695 --- 4.366 11/64 --- 0.1720 17 4.394 --- --- 0.1730 16 4.496 --- --- 0.1770 --- 4.500 --- --- 0.1772 15 4.572 --- --- 0.1800 14 4.623 --- --- 0.1820 13 4.469 --- --- 0.1850 --- 4.750 --- --- 0.1870 --- 4.763 12/64 3/16 0.1875 12 4.800 --- --- 0.1890 11 4.850 --- --- 0.1910 10 4.915 --- --- 0.1935 9 4.978 --- --- 0.1960 --- 5.000 --- --- 0.1969 8 5.055 --- --- 0.1990 7 5.105 --- --- 0.2010 --- 5.159 13/64 --- 0.2031 6 5.182 --- --- 0.2040 5 5.220 --- --- 0.2055 --- 5.250 --- --- 0.2067 4 5.309 --- --- 0.2090 3 5.410 --- --- 0.2130 --- 5.500 --- --- 0.2165 --- --- 14/64 7/32 0.2188 2 5.613 --- --- 0.2210 --- 5.750 --- --- 0.2264 1 5.791 --- --- 0.2280 A 5.944 --- --- 0.2340 --- 5.953 15/64 --- 0.2344 --- 6.000 --- --- 0.2362 B 6.045 --- --- 0.2380 --- 6.100 --- --- 0.2402 C 6.147 --- --- 0.2420 --- 6.200 --- --- 0.2441 D 6.248 --- --- 0.2460 --- 6.250 --- --- 0.2461 E 6.350 16/64 1/4 0.2500 --- 6.500 --- --- 0.2559 F 6.528 --- --- 0.2570 --- 6.600 --- --- 0.2598 G 6.629 --- --- 0.2610 --- 6.747 17/64 --- 0.2656 --- 6.750 --- --- 0.2657 H 6.756 --- --- 0.2660 --- 6.800 --- --- 0.2677 I 6.909 --- --- 0.2720 --- 7.000 --- --- 0.2756 J 7.036 --- --- 0.2770 --- 7.100 --- --- 0.2795 K 7.137 --- --- 0.2810 --- 7.144 18/64 9/32 0.2813 --- 7.250 --- --- 0.2854 --- 7.300 --- --- 0.2874 L 7.366 --- --- 0.2900 --- 7.400 --- --- 0.2913 M 7.493 --- --- 0.2950 --- 7.500 --- --- 0.2953 --- 7.541 19/64 --- 0.2969 --- 7.600 --- --- 0.2992 N 7.671 --- --- 0.3020 --- 7.750 --- --- 0.3051 --- 7.938 20/64 5/16 0.3125 --- 8.000 --- --- 0.3150 O 8.026 --- --- 0.3160 --- 8.100 --- --- 0.3189 --- 8.200 --- --- 0.3228 P 8.204 --- --- 0.3230 --- 8.250 --- --- 0.3248 --- 8.300 --- --- 0.3268 --- 8.334 21/64 --- 0.3281 Q 8.433 --- --- 0.3320 --- 8.500 --- --- 0.3346 R 8.611 --- --- 0.3390 --- 8.700 --- --- 0.3425 --- 8.731 22/64 11/32 0.3438 --- 8.750 --- --- 0.3445 S 8.839 --- --- 0.3480 --- 9.000 --- --- 0.3543 T 9.093 --- --- 0.3580 --- 9.128 23/64 --- 0.3594 --- 9.250 --- --- 0.3642 U 9.347 --- --- 0.3680 --- 9.500 --- --- 0.3740 --- 9.525 24/64 3/8 0.3750 V 9.576 --- --- 0.3770 --- 9.600 --- --- 0.3780 --- 9.700 --- --- 0.3819 --- 9.750 --- --- 0.3839 --- 9.800 --- --- 0.3858 W 9.804 --- --- 0.3860 --- 9.922 25/64 --- 0.3906 --- 10.000 --- --- 0.3937 X 10.080 --- --- 0.3970 --- 10.084 --- --- 0.4016 Y 10.260 --- --- 0.4040 --- 10.490 26/64 13/32 0.4063 Z 10.490 --- --- 0.4130 --- 10.500 --- --- 0.4134 --- 10.716 27/64 --- 0.4219 --- 11.000 --- --- 0.4331 --- 11.112 28/64 7/16 0.4375 --- 11.500 --- --- 0.4528 --- 11.509 29/64 --- 0.4531 --- 11.906 30/64 15/32 0.4688 --- 12.000 --- --- 0.4724 --- 12.200 --- --- 0.4803 --- 12.303 31/64 --- 0.4844 --- 12.500 --- --- 0.4921 --- 12.700 32/64 1/2 0.5000 --- 12.800 --- --- 0.5039 --- 13.000 --- --- 0.5118 --- 13.097 33/64 --- 0.5156 --- 13.494 34/64 17/32 0.5312 --- 13.500 --- --- 0.5315 --- 13.891 35/64 --- 0.5469 --- 14.000 --- --- 0.5512 --- 14.288 36/64 9/16 0.5625 --- 14.500 --- --- 0.5709 --- 14.684 37/64 --- 0.5781 --- 15.000 --- --- 0.5906 --- 15.081 38/64 19/32 0.5938 --- 15.478 39/64 --- 0.6094 --- 15.500 --- --- 0.6102 --- 15.875 40/64 5/8 0.6250 --- 16.000 --- --- 0.6299 --- 16.272 41/64 --- 0.6406 --- 16.500 --- --- 0.6496 --- 16.669 42/64 21/32 0.6563 --- 17.000 --- --- 0.6693 --- 17.066 43/64 --- 0.6719 --- 17.462 44/64 11/16 0.6875 --- 17.500 --- --- 0.6890 --- 17.859 45/64 --- 0.7031 --- 18.000 --- --- 0.7087 --- 18.256 46/64 23/32 0.7188 --- 18.500 --- --- 0.7283 --- 18.653 47/64 --- 0.7344 --- 19.000 --- --- 0.7480 --- 19.050 48/64 3/4 0.7500 --- 19.447 49/64 --- 0.7656 --- 19.500 --- --- 0.7677 --- 19.844 50/64 25/32 0.7813 --- 20.000 --- --- 0.7874 --- 20.241 51/64 --- 0.7969 --- 20.500 --- --- 0.8071 --- 20.638 52/64 13/16 0.8125 --- 21.000 --- --- 0.8268 --- 21.034 53/64 --- 0.8281 --- 21.431 54/64 27/32 0.8438 --- 21.500 --- --- 0.8465 --- 21.828 55/64 --- 0.8594 --- 22.000 --- --- 0.8661 --- 22.225 56/64 7/8 0.8750 --- 22.500 --- --- 0.8858 --- 22.622 57/64 --- 0.8906 --- 23.000 --- --- 0.9055 --- 23.019 58/64 29/32 0.9062 --- 23.416 59/64 --- 0.9219 --- 23.500 --- --- 0.9252 --- 23.812 60/64 15/16 0.9375 --- 24.000 --- --- 0.9449 --- 24.209 61/64 --- 0.9531 --- 24.500 --- --- 0.9646 --- 24.606 62/64 31/32 0.9688 --- 25.000 --- --- 0.9843 --- 25.003 63/64 --- 0.9844 --- 25.400 64/64 1 1.0000 Understanding Gauge Sizing Gauge sizing directly determines drill bit diameter and affects your selection in three key ways. Precision: the number and letter gauge system offers a high degree of precision for smaller drill bits — critical when exact hole dimensions matter. Compatibility: many fasteners and components are specified by gauge size, so the drill bit must match the gauge of the intended component for a proper fit. Standardisation: gauge sizing provides a consistent method for specifying drill bit dimensions across industries, making communication and cross-referencing straightforward. Selecting the Right Drill Bit The right drill size is not always fixed — it depends on several variables. The material being drilled (steel, aluminium, plastic, timber) affects which size and type of bit to use. The desired thread depth determines the clearance needed for the tap. The required thread fit — close, medium, or free — influences the drill size. Different tap types (taper, plug, bottoming) also require slightly different drill sizes. For fluteless or thread-forming taps specifically, the Engineers Black Book recommends using a good cutting oil or lubricant rather than coolant. If you need complete size data including metric and thread sizes from 0.100mm up to 101.6mm (4 inches), the Engineers Black Book (3rd Edition — Metric) is worth having on hand. Note: this table covers a broad range of sizes but may not include every available drill bit size. Always consult a detailed chart for precision applications. Drill Bit Selection by Material Drilling the right hole isn't just about the diameter — it's about matching the drill bit material and geometry to what you're cutting. The wrong combination means broken bits, oversized holes, work-hardened steel, or burnt edges. Here's what the AIMS workshop crew reaches for: Mild steel (most common) Drill: Sutton D101 Silver Bullet HSS jobber for occasional / hobby work. Sutton D102 Blue Bullet (steam-oxide finish) for production drilling — the oxide finish helps swarf release. Geometry: Standard 118° split point. Lubricant: Any general-purpose cutting fluid or Tap Magic Original. Stainless steel (304, 316) Drill: Cobalt drill bit — Sutton D108 (cobalt jobber, colour-temp tempered) or D109 (heavy duty cobalt bulk pack). The 5-8% cobalt content keeps the drill sharp through stainless's work-hardening. HSS bright drills will glaze the hole, work-harden the steel, and snap. Geometry: 130° to 135° split point preferred (sharper attack angle handles work-hardening better). Lubricant: Tap Magic for Stainless — specifically formulated. Aluminium, brass, copper, plastics Drill: Standard HSS Sutton D101 is fine for most. Sutton D113 Blue Bullet Long Drill for deeper holes. Some users prefer a higher helix angle drill for soft non-ferrous materials to evacuate long stringy chips. Geometry: 130° to 140° point geometry for soft materials. Lubricant: Tap Magic Aluminium variant — prevents the gummy build-up aluminium causes on standard cutting fluids. Cast iron Drill: HSS Sutton D102 Blue Bullet (steam-oxide). Cast iron is brittle and abrasive — the steam oxide finish prolongs drill life. Lubricant: Generally drilled DRY — chips are powder, not strings, so no cutting fluid needed. Hardened steel (above ~30 HRC) For anything above mild steel hardness — pre-hardened tool steels, heat-treated parts, hardfaced surfaces — call AIMS before you start. Solid carbide drills (Sutton D323/D326/D332 series) are the right answer, not HSS or cobalt. Contact us or call (02) 9773 0122 — we'll save you broken drills and damaged workpieces. Concrete, brick, masonry Drill: Tungsten-carbide-tipped (TCT) masonry drill — Sutton D600 (standard fixing, 3mm-13mm) or Sutton D601 (single brick, higher quality, up to 25mm). NOT HSS — HSS bits glaze and dull instantly on concrete. Use: Hammer drill mode required for concrete and brick. Regular rotary drilling on glazed tile only. Lubricant: None — drilled dry. Use a vacuum or compressed air to clear dust as you go. The AIMS workshop rule: Drill speed (RPM) matters more than most beginners realise. Big drill bits need SLOW speeds; small bits need fast. Wrong RPM for the size + material is the #1 cause of drill bit failure. The lathe RPM formula guide covers the maths; the cutting speeds & feeds reference gives you the Vc per material. Anchor Bolt Drill Size Chart Anchor bolts require a hole drilled into concrete, masonry, or brick before installation. The required drill bit size depends on the anchor type — sleeve anchors, wedge anchors, and drop-in anchors each have different requirements. Use a hammer drill or SDS drill with a masonry bit for all concrete anchor applications. Sleeve Anchors & Wedge Anchors (Dynabolts) For sleeve anchors and wedge anchors — including Ramset Dynabolts and equivalent brands — the drill bit diameter matches the anchor diameter. Drill the hole to the specified depth, clear the dust, then drive the anchor. Need help finding your size? Call AIMS on (02) 9773 0122 — the team can confirm stock and pick the right drill type for your material. Or browse masonry drill bits. Anchor Size Drill Bit Size Minimum Hole Depth Typical Application M6 6.0mm 40mm Light fixings, brackets M8 8.0mm 50mm Shelving, light structures M10 10.0mm 60mm Equipment bases, handrails M12 12.0mm 75mm Machinery, structural steel M16 16.0mm 90mm Heavy machinery, posts M20 20.0mm 110mm Structural anchoring M24 24.0mm 125mm Heavy structural anchoring Drop-In Anchors (Internal Thread) Drop-in anchors are flush-mount anchors used where a bolt or threaded rod is inserted after installation. The drill bit size matches the outer body diameter of the anchor — not the internal thread size. Always check the manufacturer's specification for the specific anchor being used, as outer diameters can vary slightly by brand. Internal Thread Drill Bit Size Minimum Hole Depth M6 8.0mm 30mm M8 10.0mm 40mm M10 12.0mm 50mm M12 16.0mm 60mm M16 20.0mm 80mm M20 25.0mm 100mm Chemical Anchors (Resin) Chemical anchors use a two-part resin to bond a threaded rod or rebar into concrete. The drill bit is typically 2–4mm larger than the bar diameter to allow the resin to flow and fully encapsulate the rod. Always follow the anchor manufacturer's specification for hole diameter and depth, as embedment requirements vary by resin system and load rating. Rod / Bar Diameter Drill Bit Size Notes M8 10.0mm Confirm with resin manufacturer M10 12.0mm Confirm with resin manufacturer M12 14.0mm Confirm with resin manufacturer M16 20.0mm Confirm with resin manufacturer M20 24.0mm Confirm with resin manufacturer M24 28.0mm Confirm with resin manufacturer Note: All anchor bolt applications in concrete require a hammer drill or SDS drill with a quality masonry bit. A standard drill will not achieve the required penetration depth or accuracy. Always blow or vacuum dust from the hole before installing the anchor — debris left in the hole reduces holding strength significantly. Related AIMS Selectors & Guides This page sits at the centre of AIMS's drilling tool cluster. The related selectors and selection guides below go deeper on the choices around it: Tap & Drill Bit Selector — Tap Drill Sizes — for threading work, pair this chart with the tap drill sizes Drill Bit Selection Guide — HSS vs cobalt vs carbide, jobber vs stub vs reduced shank vs annular cutter Cobalt Drill Bit Guide — when cobalt is worth the upgrade from HSS HSS vs Carbide End Mill — same material principles apply to drilling decisions Cutting Speeds & Feeds Reference — RPM and feed rate by material and drill diameter Cutting Tool Materials — HSS, cobalt, carbide, PCBN, PCD compared Cutting Tool Coatings — TiN, TiAlN, AlCrN, when each matters for drills Cutting Tool Troubleshooting — walking drills, poor finish, oversize holes, snapped tips Metric / Imperial / Gauge Conversion Master Chart — full drill bit + thread size cross-reference Or browse the full jobber drill bits range + cobalt drill bits — Sutton primary stock, Bordo and P&N alternates, masonry TCT, annular cutters and specialty drilling all in stock for next-day Australia-wide dispatch from our Milperra warehouse.Related Reference Charts Fastener Reference Chart — cross-reference bolt, nut, and screw measurements across metric, Unified Thread Standard, and British Thread Standard values, with thread pitch identification guides. Loctite Grade Selection Guide — identify the right Loctite product for your materials and surfaces. Spanner Size Chart — find the correct spanner or wrench size for your bolt or nut head, metric and imperial. Tapping Drill Size Chart — find the right pilot hole drill size before cutting threads. Covers metric coarse and fine, BSP, UNC, and UNF threads. Frequently Asked Questions What is 3/8 inch drill bit in mm? A 3/8 inch drill bit is 9.525mm. This is one of the most common sizes used for medium pilot holes in steel and timber. What is 1/2 inch drill bit in mm? A 1/2 inch drill bit is 12.7mm exactly. Used for clearance holes on M12 bolts and general large-bore drilling. What is 1/4 inch drill bit in mm? A 1/4 inch drill bit is 6.35mm. Common pilot size for 1/4-20 UNC fasteners and a workshop default for general drilling. What is 5/16 inch drill bit in mm? A 5/16 inch drill bit is 7.94mm — close enough to 8mm for most practical applications, but always use the exact size for precision work. What is 5/8 inch drill bit in mm? A 5/8 inch drill bit is 15.875mm. Used for M16 clearance holes and large structural fixings. What is 9/16 inch drill bit in mm? A 9/16 inch drill bit is 14.288mm. Often used as a clearance hole for 1/2 inch bolts. What is 3/16 inch drill bit in metric? A 3/16 inch drill bit is 4.763mm — close to 4.75mm. Common for light pilot holes in timber and sheet metal. What is 6mm drill bit in imperial? A 6mm drill bit is approximately 15/64 inch (0.2362"). It sits between 15/64" (5.953mm) and 1/4" (6.35mm) — use 6mm where the exact metric size is needed. What is 8mm drill bit in imperial? An 8mm drill bit is approximately 5/16 inch (7.94mm) — they're functionally interchangeable for most general drilling work. What is the order of drill bit sizes? Drill bit sizes run from very small to very large across four overlapping systems: number drills (#80 smallest = 0.343mm, up to #1 = 5.79mm), letter drills (A = 5.94mm up to Z = 10.49mm), fractional inches (1/64" up to 1" and beyond), and metric (typically 0.5mm up to 25mm+). Use the full chart above to cross-reference. What size drill bit do I need for a pilot hole? It depends on the screw or bolt diameter and the material being drilled. As a general rule, size the pilot hole at around 75-85% of the screw's outer diameter for timber, and closer to 90% for metal. For threaded pilot holes, refer to the Tapping Drill Size Chart, which lists the correct drill size for each thread specification. What do number and letter drill bit sizes mean? Number drills (1-80) and letter drills (A-Z) are gauge-based sizing systems used primarily in the USA and in precision engineering. Number sizes run from very small (#80 = 0.343mm) up to #1 (5.791mm), then letter sizes continue from A (5.944mm) through to Z (10.490mm). What are the most common drill bit sizes for general workshop use? For general use in Australia, the most commonly used metric sizes are 3mm, 4mm, 5mm, 6mm, 8mm, and 10mm. These cover most standard fastener pilot holes and everyday drilling tasks. A 13-piece metric set from 1.5mm to 6.5mm in 0.5mm increments is the typical starter kit. Can I substitute a fractional imperial drill bit for a metric size? In most cases yes, provided the sizes are close enough for the application. The chart shows metric and imperial sizes side by side so you can identify the nearest equivalent. For precision work — tight tolerances or threaded holes — always use the exact specified size. What is the largest drill bit size covered in this chart? This chart covers drill bit sizes up to 25.4mm (1 inch / 64/64"). For larger bore sizes, use a spade bit, hole saw, or annular cutter instead of a standard twist drill. Where can I buy drill bits in Australia? AIMS Industrial stocks HSS, cobalt, and carbide drill bits for metal, timber, masonry, and general use, available online with Australia-wide delivery. For complete metric bolt sizing (M3-M24) with thread pitch and head dimensions, see our Metric Bolt Size Guide. People Also Ask — Drill Bit Size Chart: Metric, Imperial & Fractional Q: What size drill bit do I need for an M8 tap? For an M8 × 1.25 coarse thread, use a 6.8 mm drill bit. For M8 × 1.0 fine thread, use a 7.0 mm bit. Always check the specific pitch before drilling — the wrong pilot hole size is the most common cause of tap breakage or stripped threads. Q: How do I convert metric drill bits to imperial? Divide the metric diameter by 25.4 to get inches, or multiply inches by 25.4 to get millimetres. For example, a 10 mm bit equals 0.394" (closest imperial equivalent is 25/64"). A drill bit conversion chart saves calculation errors on the job. Q: What drill bit size is closest to 1/4 inch in metric? A 1/4" drill bit is exactly 6.35 mm. The closest standard metric size is 6.0 mm (slightly under) or 6.5 mm (slightly over). For clearance holes, 6.5 mm is usually the better choice; for tap pilot holes, refer to the thread specification instead. Q: What are the standard drill bit sizes in mm? Standard metric drill bit sets typically cover 1.0–13.0 mm in 0.5 mm steps, with jobber sets often including 0.5–13 mm in 0.1 mm increments. Common sizes for general trade work are 3, 4, 5, 6, 6.5, 8, 10, and 12 mm. Fractional sets cover 1/16" to 1/2" in 1/64" steps. See AIMS's full carbide drill bits range — trade pricing and Australia-wide despatch. Need machining? Browse the AIMS range at machining.
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