Product Guides
Indexable Insert Guide: ISO 1832 Codes, Grades, Coatings & Brand Cross-Reference for Australian Workshops
Indexable inserts: ISO 1832 designation decoded, ISO 513 grade system, SECO vs Sandvik vs Iscar vs Kennametal cross-reference for Australian workshops.
Read moreProduct Guides
Surface Roughness Guide: Ra Rz, ISO 21920 & Mitutoyo Surftest
Surface roughness: Ra/Rz/Rsm parameters, ISO 21920-2:2021 transition, machining process Ra targets and Mitutoyo Surftest profilometers for AU workshops.
Read more
HSS vs. Carbide: Quick Reference Guide
Choosing between High-Speed Steel (HSS) and carbide tools depends on your machining needs, materials, and production requirements. Here’s a breakdown to help you decide. Quick Comparison: HSS vs. Carbide Feature HSS (High-Speed Steel) Carbide Durability Tougher, resists chipping, good for varied applications Harder but more brittle, best for stable setups Speed Suitable for lower-speed operations Designed for high-speed machining Lifespan Wears faster but can be resharpened Lasts longer without losing sharpness Cost More affordable, great for small production runs Higher upfront cost, better for large-scale jobs Best Use General-purpose drilling, tapping, and milling High-precision and high-volume machining Choosing the Right Tool: Key Factors 1. Work Volume & Cost ✓ High production & hard materials? Carbide lasts longer and performs better at high speeds.✓ Occasional machining? HSS is more affordable and can be resharpened. Popular HSS Tools Popular Carbide Tools HSS Jobber Drill Bits Carbide Rotary Burrs HSS Step Drills Carbide Tipped Annular Cutters 2. Material Hardness ✓ HSS: Best for mild steel, aluminum, and softer alloys.✓ Carbide: Ideal for stainless steel, cast iron, and hardened materials. Best Tools for Mild Steel & Aluminum: Best Tools for Stainless Steel & Harder Materials HSS Hole Saws Carbide End Mills HSS Taps & Dies Tungsten Carbide Lathe Inserts 3. Speed vs. Tool Life ✓ Carbide: Runs at higher speeds, stays sharper longer.✓ HSS: Wears faster but can be resharpened to extend its life. High-Speed Cutting Tools Tools for Longer Lifespan Carbide Hole Saws Solid Carbide Drill Bits 4. Machine Setup & Rigidity ✓ Less stable setup? HSS is more forgiving and resists chipping.✓ High-precision, rigid machines? Use carbide to avoid breakage. Rigid & Precision Machining Tools Carbide Micro Drills Carbide Countersinks 5. Surface Finish & Precision ✓ HSS: Good for general machining but may require secondary finishing.✓ Carbide: Provides a smoother finish and holds tighter tolerances. Smooth & Precise Cutting Tools Carbide-Tipped Router Bits Carbide Slitting Saws 6. Cooling & Lubrication ✓ HSS: Needs cutting fluids to reduce wear.✓ Carbide: Can be used dry, but lubrication improves lifespan. Coolants & Lubrication Supplies Cutting Fluids & Coolants Coolant Hoses & Systems 7. Application-Specific Advice Application Best Choice Recommended Tools Drilling HSS for general use, carbide for high-speed drilling HSS Jobber DrillsCarbide Annular Cutters Milling Carbide for precision & speed, HSS for low-speed operations HSS End MillsCarbide Router Bits Tapping HSS for most tasks, carbide for production & hard materials HSS Taps & DiesCarbide Threading Inserts Other Tips: If speed, precision, and durability are your top priorities, invest in carbide tools. If you need an affordable, flexible option that can be resharpened, HSS is the way to go. Shop All Machining Tools: Browse our full range here People Also Ask — HSS vs. Carbide: Quick Reference Guide Q: When should I use carbide tooling instead of HSS? Choose carbide when cutting hardened materials (above 45 HRC), high-speed production where tool changes are costly, abrasive materials (cast iron, fibreglass), or when surface finish requirements are tight. HSS remains the better choice for interrupted cuts on a manual lathe, low-volume workshop work, and materials that are prone to carbide chipping — such as some titanium alloys and work-hardened stainless steel. Q: Why do carbide drill bits break so easily? Carbide is extremely hard but brittle — it fails suddenly under shock loading or lateral force rather than bending as HSS does. Common causes of carbide breakage: drilling without centre-drilling first (the bit deflects on entry), insufficient rigidity in the setup, drilling too slowly (generates heat), using hand-feed on manual machines (uncontrolled infeed), or selecting carbide for interrupted or cross-hole drilling where HSS is more appropriate. Q: Are Sutton Tools drill bits made in Australia? Yes — Sutton Tools manufactures its HSS and HSS-Co (cobalt) drill bits in Melbourne, Victoria, making them one of Australia's few remaining domestic cutting tool manufacturers. Sutton's M35 (5% cobalt) and M42 (8% cobalt) drills are well-regarded for stainless steel, Inconel, and other difficult-to-machine materials. Australian-made tooling also simplifies supply chain for businesses with local content requirements. Q: Can HSS tooling be resharpened? Yes — HSS drills, end mills, and lathe tools can be resharpened repeatedly by an experienced tool grinder, extending their useful life significantly. Carbide can also be reground, but requires diamond wheels and is typically only economical for larger tooling. For high-volume workshops, a tool grinding service contract is often more cost-effective than replacing worn HSS tooling outright.
Read moreBoring Bar Guide: Sizes, Indexable & Selection
Boring bars: indexable vs solid carbide, L:D ratio, insert geometry (CCMT/DCMT/TPMT), centre height and chatter control for Australian workshops.
Read moreKnurling Guide: Patterns, Pitches & Lathe Technique
Knurling: cut vs form, DIN 82 patterns, pitch selection, RPM and feed rates, workpiece diameter calculation and tool selection for Australian workshops.
Read moreLathe RPM Formula Guide
Lathe RPM: the formula in metric and imperial, cutting speeds by material, CSS vs G97, facing-cut math and chuck speed limits for Australian workshops.
Read moreER Collet Guide: ER11–ER50 Sizes, Capacity & Runout
ER collets are the most widely used clamping system on machining centres worldwide. They handle drills, end mills, taps, reamers, boring tools and probes across hobby benchtop CNC mills right up to 50 kW production VMCs. Despite their ubiquity, ER collets are also the most misunderstood tool-holding system in the workshop — runout figures vary by an order of magnitude between brands, the "1 mm clamping range" rule has more nuance than spec sheets suggest, and the question of whether end mills belong in ER collets generates more heated forum debate than almost any other machining topic. This guide covers the full ER series from ER8 to ER50, the DIN 6499 standard that defines them, runout in plain numbers, the difference between standard and ball-bearing ER nuts, when ER beats R8 or 5C and when it doesn't, installation technique that actually matters, and the forum-validated truth on common questions. This article is part of our reference content drawn from the Engineer's Black Book — a workshop-floor reference covering tolerances, drill sizes, threads, materials and clamping data including ER collets. What is an ER collet (and why "ER")? An ER collet is a slotted, tapered steel sleeve that grips a tool shank when compressed by a threaded nut against a matching tapered seat in the spindle, toolholder or chuck. The 8° included taper closes the slits and clamps the tool concentrically. The "ER" designation comes from REGO-FIX, the Swiss company that developed the system in 1973. The patent has long expired and the geometry is now codified internationally as DIN 6499 / ISO 15488, so the system is open and produced by hundreds of manufacturers — but the "ER" naming convention stuck. The number after ER refers to the major diameter of the collet body in millimetres: an ER32 collet has a 33 mm major diameter (the numbers are nominal, not exact), an ER25 has 26 mm, and so on. What makes ER different from earlier collet systems (5C, R8, MT) is the dual-angle nut design. The thread on the nut pulls the collet into the holder taper while a 30° eccentric ring on the front of the nut engages a matching groove on the collet — so removing the nut from the holder also extracts the collet automatically. This single feature is why ER dominates: tool changes are fast, repeatable, and don't require a knockout bar. ER collet sizes — full ER8 to ER50 reference Eight sizes are defined in DIN 6499. The capacity range column is the maximum tool shank the collet will accept; the minimum is the maximum minus the clamping range (1 mm for most sizes; see capacity section below). Series Major Ø (mm) Length (mm) Max capacity (mm) Typical use ER8 8.5 13.6 5 Engraving, watchmaking, micro-drilling ER11 11.5 18 7 Hobby CNC routers, PCB drilling, dental ER16 17 27.5 10 Benchtop CNC, light milling, wood routers ER20 21 31.5 13 Light production, spindle attachments, drilling ER25 26 34 16 Hobby/light production milling, wood routers ER32 33 40 20 The workhorse — small/medium VMCs, lathe live tooling ER40 41 46 26 Larger VMCs, bigger end mills, drilling ER50 52 60 34 Heavy-duty milling, large VMCs, manual mills Most common in Australian workshops: ER32 dominates production. Most BT30, BT40, ISO30, HSK63A, R8 and even Tormach TTS toolholders are available in ER32. ER25 is the runner-up for smaller machines. ER11 and ER16 dominate hobby CNC and wood routing (Shapeoko, Carbide 3D, Avid CNC, Stepcraft and similar use these almost exclusively for their stock spindles). ER collet anatomy and how it clamps A standard ER collet has three functional surfaces: The 8° external taper — matches the seat in the toolholder or spindle. This converts axial pull into radial clamping force on the bore. The slits — alternating slits cut from each end allow the bore to close on the tool. ER collets are slit so half the slits are open at the front and half at the rear, giving balanced clamping along the length. The 30° eccentric groove at the small end of the collet — engages with a corresponding ring inside the ER nut. This is what extracts the collet when the nut is loosened. The bore is precision-ground to the nominal size minus the maximum clamping deflection. When the collet is unloaded the bore is roughly the maximum capacity; under nut torque the slits close and the bore reduces uniformly to grip the tool. Standard ER collets have a bore tolerance of around H6 with concentricity to the taper of 5–10 μm on quality collets. One thing to understand: the collet does not clamp at a single point. The 8° taper distributes the gripping load across the full collet length, which is why ER collets resist tool slip well in axial pull-out conditions (typical of drilling and tapping) but are less rigid radially than a side-lock holder or a Weldon flat — which becomes relevant when we discuss end mills. Collet capacity range — the 1 mm rule (and the truth) DIN 6499 defines the standard clamping range of an ER collet as 1 mm: an ER32-16 collet will hold any tool from 15 mm to 16 mm shank diameter. So you need a separate collet for every millimetre of shank size. This is where forum confusion peaks. Three points worth understanding: The 1 mm range is real, but quality drops at the extremes. Practical Machinist consensus is that runout and grip both degrade noticeably in the bottom 0.3 mm of the range. A 16 mm collet clamping a 15.05 mm shank will runout worse than the same collet on a 15.95 mm shank, because the slits close further and the geometry distorts. For best accuracy, size your collet so the shank is in the upper half of the range. Some ER collets claim 1.5 mm or even 2 mm range. These exist (often badged as "extended range" or "flexible") and they do clamp, but runout is materially worse. Avoid for precision work. Imperial collets are not the same as metric. ER collets in fractional inch sizes (1/4", 3/8", 1/2", 3/4", etc.) are made in the same major-diameter series but with imperial bore sizes. A 1/2" collet is 12.7 mm — not the same as a 13 mm collet. Don't substitute one for the other on precision work; the runout penalty is real. Hard rule: never undersize a collet to clamp a smaller tool. A 12 mm shank in a 12-11 mm collet (range 11–12) will clamp; the same 12 mm shank in a 13–12 collet trying to "stretch" 1 mm undersize will either not grip or destroy the collet. The slits don't close that far evenly. DIN 6499 / ISO 15488 — the standard explained DIN 6499 is the German standard that defines ER collets. ISO 15488 is the international equivalent (the two are essentially harmonised). Both specify: Major and minor diameters for each ER series (ER8 through ER50) The 8° collet body taper The 30° pull-out groove geometry Bore tolerances and runout limits Slot configuration (number, depth, alternating pattern) Three tolerance classes are defined in DIN 6499: Class Max runout at 3×D from collet face Typical use Standard (DIN 6499 Class 2) ≤ 15 μm General machining, drilling, light milling High precision (Class 1, often labelled "AA" or "Ultra") ≤ 10 μm Reaming, finishing, tight-tolerance work Premium / matched-pair (varies by maker) ≤ 5 μm or sub-5 μm Aerospace, mould tooling, micro-machining Cheap ER collets sold in eBay/AliExpress sets often runout at 25–50 μm or worse — well outside any DIN class. They will function for hobby work and rough drilling but are unsuitable for precision milling. Forum-validated reality on Practical Machinist: a $400 set of 18 ER32 collets with documented sub-10 μm runout is a different product to a $60 set of 18 ER32 collets sold as "DIN 6499 compliant" — the latter is rarely tested and the runout claim is rarely honoured. Runout — the major pain point Runout is the radial deviation between the rotational axis of the spindle and the rotational axis of the tool tip when the assembly is rotating. It is the single biggest determinant of: Hole size accuracy (a drill with 30 μm runout will produce a hole 60 μm oversize) Surface finish in milling and reaming Tool life — uneven loading on cutting edges accelerates failure Chatter — runout amplifies vibration at high speeds and small step-overs Runout in an ER collet assembly is the cumulative result of: Spindle runout — the machine itself Toolholder runout — how true the holder runs in the spindle taper Holder bore taper accuracy — the quality of the seat the collet sits in Collet runout — how concentric the bore is to the taper Nut squareness — how square the nut clamps the collet Tool shank tolerance — h6 vs h7 vs uncontrolled A typical good-quality production CNC will have spindle runout under 5 μm. A quality BT40 ER32 toolholder adds another 3–5 μm. A premium collet adds 3–5 μm. A premium ground-shank end mill (h6) adds another 2–3 μm. Total realistic stack-up at the cutting edge: 10–15 μm for a well-set-up ER assembly. Hobby CNC reality: Tormach Tooling System (TTS) ER collets stacked in an R8 spindle on a manual mill conversion can easily measure 30–60 μm runout total. Not because any single component is bad, but because the errors stack. This is fine for woodworking, hobby milling, drilling and rough work — but it is the limiting factor for precision finishing on these machines. How to actually measure it: chuck a precision test bar (h5 or h6 ground rod) into the collet, set up a dial test indicator (DTI) against the bar at 3× the collet face distance, and rotate the spindle by hand. The full-indicator reading (FIR) is your assembly runout. Don't measure on the cutting flutes of a tool — they're not symmetrical. ER nuts: standard vs ball-bearing (high-precision) The ER nut is a precision-ground tapered nut with internal threads. It comes in two main styles: Standard ER nut. Uses a hardened, ground steel ring engaged in the eccentric groove on the collet. Tightening the nut forces this ring against the back of the groove, pulling the collet into the holder taper. Cheap, simple, durable. Common to all suppliers. Requires correct torque to achieve full clamping force; under-torqued nuts cause tool pull-out, over-torqued nuts distort the collet and increase runout. Ball-bearing ER nut (high-precision nut, "Hi-Q", "Power Nut", "Mega Nut", "PowerGrip", "Hi-LOK" depending on manufacturer). Replaces the steel ring with a small angular contact bearing. The ball bearing rolls on the eccentric groove as the nut is tightened, eliminating the friction at that interface. Effects: Lower torque needed for the same clamping force — typically 30–40% less. More uniform clamping — no friction-induced tilt of the nut, so squareness is better. Reduced runout — published claims of 50% improvement, which forum-validated testing on Practical Machinist puts closer to 20–30% in practice — still a meaningful gain. Higher gripping force at safe torque — better resistance to end-mill pull-out under heavy radial cutting. The premium for a ball-bearing ER nut is real — typically 4–8× the cost of a standard nut. For aerospace, mould-and-die, or any work where finishing surface finish matters, it pays for itself quickly. For drilling, tapping and rough milling, the standard nut is fine. Important: ball-bearing nuts and standard nuts both fit the same collets. You can swap nut styles without changing the collet inventory. Sealed (coolant-through) and tap collets Sealed ER collets have a rubber or PU sealing ring at the back of the collet. They're used with through-coolant toolholders to prevent coolant leaking past the collet at any pressure above about 5 bar. Standard ER collets will leak coolant at 10–70 bar (typical CT through-coolant pressures), starving the cutting edge. If you have a through-coolant capable holder and machine, sealed collets are mandatory for that benefit. Sealed collets have slightly higher runout than non-sealed (the seal adds a stack-up term), so they're a working compromise. Use them only where you actually need coolant through. ER tap collets are designed for tapping. They come in two flavours: Square-drive tap collets — bore is round at the front for the tap shank but has a square section at the back to engage the tap's square drive end. Stops the tap slipping under cutting torque. Also called "Whistle Notch" tap collets in some catalogues. Compensating (tension/compression) tap holders — these are usually a separate ER-style assembly with axial float built in, used with rigid tapping cycles on machines without true synchronous tapping. Float compensates for the small mismatch between feed and pitch. For modern CNCs with rigid tapping, the square-drive ER tap collet alone is usually sufficient. For older machines, the floating tap holder is still common. Premium vs budget — the price-to-runout reality This is the most-asked forum question for hobbyists and small shops, and the answer is more nuanced than "buy the expensive one." Tier Typical price (ER32 set of 18) Typical runout Suitable for Budget (eBay, AliExpress, no-name) AU$50–120 20–60 μm Hobby CNC, wood, soft metals, drilling, rough work Mid-range (Vertex, Glacern, generic Taiwan) AU$200–400 10–20 μm General production milling, light precision work Premium named (Sandvik, Iscar, Lyndex, Schunk) AU$700–1,500 5–10 μm Production precision, aerospace-tier, finishing Top-tier (REGO-FIX PowerGrip, Lyndex-Nikken, Schunk Tendo) AU$1,500–3,500 ≤ 5 μm, often ≤ 3 μm Mould tooling, micro-machining, sub-5 μm work Forum-validated truth (Practical Machinist consensus across multiple long-running threads): the jump from budget to mid-range gives the biggest practical improvement. The jump from mid-range to premium is real but only matters if your spindle, holder and tool are also at premium tier — otherwise the premium collet is being held back by the rest of the stack-up. For a hobby CNC, 25 μm runout is invisible at 0.5 mm step-over in plywood. For a 0.001"-tolerance bore in stainless steel, even 5 μm matters. Buy individually for the sizes you actually use. Don't buy a full 18-piece set in budget tier and then have to replace your three most-used sizes with mid-range. Buy mid-range or premium for ER25-13/16/20 (or whichever shanks you live in), and budget for the sizes you rarely touch. End mills in ER collets — the great debate This is the single most-discussed ER collet question on every machining forum. The 170+ comment thread on r/Machinists titled "Opinions on endmills in ER collets" captures the full split. The honest answer is more nuanced than either extreme. Position 1 — "ER is fine for end mills." Vast majority of small shops, hobby CNC users, and a meaningful chunk of production shops run end mills exclusively in ER. With a quality collet (≤ 10 μm runout), correct torque, and reasonable depth-of-cut, ER collets hold end mills perfectly well for general work. Tens of thousands of moulds, parts and projects produced this way every day worldwide. Position 2 — "End mills belong in dedicated holders." Side-lock (Weldon flat) holders, hydraulic holders, shrink-fit holders and milling chucks all out-perform ER collets on heavy radial cutting because they grip more rigidly without relying on friction alone. ER collets can pull tools out under aggressive cutting, especially climb milling at high radial engagement. The truth in the middle: Light to medium cutting (under 50% radial engagement, modest depth of cut) — ER is fine for end mills if torque is correct and the assembly is precision-tier. Heavy roughing, deep slotting, high radial engagement on tough materials (steel, stainless, titanium) — dedicated holders win every time. Side-lock for shanks with Weldon flats; shrink-fit or hydraulic for plain shanks; milling chuck (Schunk Tendo, Hardinge Sure-Grip) for the highest grip-force needed. Pull-out is real. Climb milling generates an axial force that tries to pull the tool out of the collet. Conventional milling pushes it in. If you're climb milling at high engagement and the cutter loosens, that's the mechanism. Always seat the end mill with the cutting flutes well clear of the collet face — don't bury cutting edges inside the collet bore. This causes premature collet wear and can shave the bore eccentric. Two practical rules from forum consensus: For 6 mm and smaller end mills, ER collets are arguably better than side-lock — the small Weldon flats on tiny shanks compromise rigidity, and ER's distributed grip works in the small-tool regime. For 12 mm and up on heavy steel cutting, get a side-lock or shrink-fit holder. ER will work but you're leaving rigidity (and metal removal rate) on the table. A common middle-ground setup in production shops: ER toolholders for finishing, shrink-fit or hydraulic for roughing. Drill bits, reamers and taps in ER collets This is where ER collets shine — and where most pull-out concerns disappear because the cutting forces are predominantly axial-into-the-work, not pulling the tool out. Drill bits — straight-shank drills (jobber, screw machine, stub) are at home in ER collets. Concentric clamping reduces hole oversize. Through-coolant drills with sealed ER collets is the production standard. Reamers — reaming is highly sensitive to runout. Use the highest-precision ER collet you can afford for reaming, ideally with a ball-bearing nut. A 0.025 mm reamed hole tolerance evaporates if total runout is 30 μm. Floating reamer holders (held in an ER) are common for reaming on machines with imperfect alignment. Taps — square-drive ER tap collets are standard. For rigid tapping on modern CNCs, the standard ER tap collet works perfectly. For tension-compression tapping, use a dedicated floating tap holder. Boring bars — small boring bars (under ~16 mm shank) live in ER collets in production. The grip is sufficient and runout is repeatable. Installation: torque, technique, common mistakes Correct ER collet installation has more subtlety than people realise. Get it wrong and you'll either lose tools or destroy collets. Step 1 — clean everything. Wipe the collet taper, the holder bore, and the inside of the nut. Chips, coolant residue or anti-seize build-up will offset the collet and increase runout dramatically. Compressed air or a clean rag, not solvents that leave a film. Step 2 — snap the collet into the nut FIRST. This is the step most often skipped by beginners. The 30° eccentric ring inside the nut must engage the matching groove on the collet before the collet goes into the holder. Hold the nut in one hand, tilt the collet at about 15°, push the small end up into the nut so the eccentric ring snaps over the groove, then rock it square. You should feel a positive click. Never put the collet into the holder first and then try to thread the nut on top — this damages the eccentric and causes pull-out failures later. Step 3 — insert the tool with the right stick-out. Cutting flutes (or drill flutes) should be clear of the collet face. Don't bury cutting edges inside the collet — they'll mark the bore. Don't run the tool too far out either — the longer the stick-out, the more deflection under cutting load. Aim for stick-out of about 2× shank diameter for general work. Step 4 — thread the nut on by hand. Make sure the threads engage cleanly. Cross-threading is rare but ruinous when it happens. Step 5 — torque to spec. Use a spanner appropriate to the nut size (slogging spanners are common, click-torque ER spanners exist for production). Approximate torque values: Series Standard nut torque Ball-bearing nut torque ER11 15–18 Nm 10–12 Nm ER16 30–40 Nm 20–25 Nm ER20 50–60 Nm 30–40 Nm ER25 70–100 Nm 40–55 Nm ER32 100–130 Nm 55–75 Nm ER40 140–170 Nm 80–100 Nm ER50 200–250 Nm 120–150 Nm Hand-tight is not enough. Forum-validated reality: most ER tool-pull-out incidents trace back to under-torqued nuts. A "good firm pull" with a 250 mm spanner on an ER32 is roughly 100 Nm — adequate. Hand-tight is around 30 Nm, which is well under spec. Common mistakes: Tightening the nut without a tool installed — the slits close uncontrolled, deforming the collet permanently. Using the wrong size collet (clamping a 10 mm shank in a 13–12 collet) — won't grip, will likely shear under load. Re-using a collet that has been used to clamp without a tool — distorted, scrap it. Cleaning collets in solvent then storing wet — flash rust on the precision surfaces. Wipe dry, store with a light oil film. Mixing different brand collets and nuts on precision work — geometry is standardised but tolerances stack. Match for best results. ER vs R8 vs 5C vs collet chuck — when to use what Five common workshop clamping systems, each with strengths: System Best for Capacity Tool change Runout (typical) ER VMC tool changing, drilling, light/medium milling, taps 0.5–34 mm depending on series Fast (snap-in nut) 5–15 μm R8 Manual milling machines (Bridgeport-style) 1.5–20 mm typical Slow (drawbar from above) 10–25 μm 5C Lathe workholding, second-op fixturing, indexing 1.5–28 mm Slow (drawbar) 10–25 μm Side-lock (Weldon) End mills with flats — heavy roughing Discrete sizes only Fast (set screw) 5–15 μm but ZERO axial pull-out Hydraulic / shrink-fit Precision finishing, high RPM, tight runout Discrete sizes (must match shank) Hot work for shrink-fit; bolt for hydraulic ≤ 3 μm achievable R8 is a single-angle taper used in Bridgeport-style manual mills. R8 collets are simple — a taper with a thread for the drawbar, no nut. Common, cheap, lower precision than ER. Many R8 spindles have an ER toolholder fitted with a drawbar — best of both worlds for hobby CNC conversions. 5C is a workholding collet (lathe) — gripping the workpiece, not a tool. ER and 5C aren't competing systems; they do different jobs. Side-lock holders use a Weldon flat on the tool shank — a setscrew clamps directly into the flat. Zero pull-out under any cutting load, but you need tools with the matching flat. Common for end mills above 12 mm in production. Hydraulic and shrink-fit are the precision-finishing answer. Hydraulic holders use oil pressure inside a thin steel sleeve to clamp the tool; shrink-fit heat-expands the holder, drops the tool in, and contracts to grip on cooling. Both achieve sub-3 μm runout reliably. Expensive, slow to change tools, but unmatched for finishing accuracy. Practical recommendation: ER is the right answer for 80% of typical workshop work. Add side-lock holders for heavy end milling at 12 mm+ shank; add hydraulic or shrink-fit if you're chasing sub-5 μm runout for finishing. Don't replace ER with anything — extend it. Applications by machine type Hobby CNC routers (Shapeoko, Carbide 3D, Avid, Stepcraft, Onefinity). ER11 dominates because most stock spindles are 1.5–2.2 kW with ER11 native. ER16 on bigger spindles and the higher-end builds. Budget collets are fine for wood; mid-range becomes worthwhile for aluminium. Benchtop CNC mills (Tormach, Sherline, Taig, PCNC). Tormach Tooling System (TTS) is essentially ER20 in a 3/4" stub holder, drawn into an R8 spindle. Most Tormach owners run almost everything in TTS-ER20. Sherline and Taig are typically smaller — ER16 territory. R8 manual mills converted to CNC. ER32 in an R8 toolholder is the most common setup. Wide capacity, fast tool change, good enough runout for most work. Production VMCs (Haas, DMG Mori, Doosan, Mazak). BT30, BT40, HSK63A are common spindle types. ER32 collet chucks are universal. Most shops run ER for all drilling, tapping, light milling — and dedicated holders for heavy roughing and finishing. Lathe live tooling. Driven tools on CNC lathes use ER collet attachments for drilling and milling stations. ER32 typical; ER25 on smaller machines. Engraving and PCB work. ER8 and ER11 dominate. Tiny tool diameters, very high RPM (often 24,000–60,000 RPM). Premium collets here are mandatory — runout magnifies at small diameters. Common mistakes and how to avoid them Putting the collet in the holder before snapping it into the nut. The eccentric ring needs to engage the collet groove FIRST. Skipping this damages the geometry over time. Tightening the nut without a tool inserted. Crushes the slits. Permanent damage. Under-torquing the nut. Hand-tight is not enough. Use a spanner. Tools pull out. Surface finish suffers. Over-torquing the nut. Distorts the collet, increases runout. Stay within published torque values. Mismatched collet and tool size. Don't undersize a collet to clamp a smaller tool. Get the right collet. Dirty taper or bore. Single biggest cause of unexpected runout. Wipe everything before assembly. Using budget collets for precision finishing. 30 μm runout on a finish reamer makes the whole reaming exercise pointless. Ignoring the eccentric groove on used collets. If the groove is worn or chipped, the collet won't extract properly and may slip under load. Inspect on every use. Storing collets loose in a bin. They knock about, the precision surfaces scuff. Use a holder or tray. Mixing brand nuts with brand collets without checking. Tolerances are standardised, but not perfectly. For precision work, match. A note on AIMS and ER collets AIMS Industrial does not currently stock ER collets — they're a specialist precision-tool category dominated by REGO-FIX, Lyndex-Nikken, Schunk and Iscar through specialist tool suppliers. We don't pretend otherwise. Where we can help is the surrounding workshop categories — drill bits, end mills, taps, reamers, cutting fluids, hand tools, measuring equipment, safety gear and PPE. If you have a precision tooling question that crosses into territory we cover, give us a call on (02) 9773 0122 or use our contact page. For deeper reference content on tool clamping, tolerances, threads and machining data, the Engineer's Black Book is one of the most-used workshop references in Australian machine shops — small enough to live in the toolbox, comprehensive enough to answer most floor-level questions. Pair this with our Tap Types guide — the spiral point vs spiral flute distinction matters more than most tradies realise. For grub screws (cup, cone, flat point — metric and imperial), see our grub screws range. Need metric spiral point taps? Browse the AIMS range at metric spiral point taps. Share: Share on Facebook Share on X Pin on Pinterest Previous Post Cobalt Drill Bit Guide: M35, M42 Grades, When to Use, and How to Choose Next Post Flow Meter Guide: Types, Oval Gear vs Turbine, and Choosing for Diesel, Petrol, Oil & AdBlue Dispensing Related Posts bordo Reciprocating Saw Blade Guide: TPI Selection, Bi-Metal vs Carbide, Wood/Metal/Demolition Blade Choice May 11, 2026 AIMS Industrial bsp Grease Nipple & Zerk Fitting Guide: Thread Sizes, Types, BSP vs UNF & How to Identify May 11, 2026 AIMS Industrial bolt-extractor Bolt Extractor Guide: Easy-Outs, Spiral Flute, Multi-Spline & Bolt Extractor Sockets May 11, 2026 AIMS Industrial People Also Ask — ER Collets Q: What does the ER designation mean in ER collets? ER collets take their name from the German word 'Erohrspannzange' — essentially 'expansion collet' — and the system was developed to provide a versatile, standardised clamping solution for CNC machining centres. The number following ER indicates the collet's outer diameter in millimetres — so ER32 has a 32 mm outer diameter and ER16 has a 16 mm outer diameter. The ER designation is now an international standard under DIN 6499 / ISO 15488 and is the most widely used toolholding system on machining centres worldwide. Q: What is the 1 mm clamping range rule for ER collets? Each ER collet is nominally sized for a specific shank diameter, but it can clamp tools with a shank diameter up to approximately 1 mm smaller than its nominal size. This means a 10 mm ER collet can grip shanks from 10 mm down to 9 mm. The collet should not be used to clamp a shank larger than its nominal size, as this overstresses the collet and destroys it. For best accuracy and longest collet life, use a collet matched as closely as possible to the actual shank diameter rather than relying on the full 1 mm range. Q: What is runout in an ER collet system and how is it measured? Runout is the amount by which the centreline of the clamped tool deviates from the centreline of the spindle during rotation, measured in microns (thousandths of a millimetre) at a set distance from the collet face. High runout causes dimensional inaccuracy in the machined part, premature cutting edge wear, and surface finish degradation. Runout in an ER system is affected by the quality of the collet, the nut, the toolholder, and how clean the mating surfaces are. Standard ER collets typically achieve 5–10 microns TIR; high-precision collets can achieve 2–3 microns or better. Q: What is the difference between a standard ER nut and a ball-bearing ER nut? A standard ER nut draws the collet into its taper using sliding friction as the nut is tightened. A ball-bearing ER nut replaces this sliding contact with a ball thrust bearing between the nut face and the collet flange. This allows the nut to be tightened to higher torque without imparting the same rotational friction to the collet, resulting in more consistent clamping force, better runout, and longer collet life. Ball-bearing nuts are recommended for high-precision work or where consistent tool projection is critical.
Read moreShoulder Bolt Guide: Sizes, Specifications and Applications
Shoulder bolts: ISO 7379 sizing, Grade 12.9 alloy steel, H7/h6 shoulder fit, pivot vs spacer applications, and metric vs imperial selection guide.
Read more
How to Remove a Broken Tap: Methods, Tools & Prevention
Stop — Read This Before You Touch the Workpiece A broken tap feels like a crisis. The instinct is to grab the nearest drill bit and go. That instinct destroys more parts than the broken tap ever would. HSS taps are harder than HSS drill bits. Driving a standard twist drill into a broken tap will snap the drill and press the tap fragments deeper and tighter into the hole. Once you've done that, your options narrow significantly. The first rule of broken tap removal: do nothing until you have assessed the situation and chosen the right method. Two minutes of assessment can save hours of work — or a scrapped part. If the broken fastener is a stud rather than a tap — different geometry, different tool family — see our Stud Extractor Guide for cam-grip, collet, and spiral hex extractor selection plus the heat-the-parent-not-the-stud removal technique. Assess Before You Act Work through these questions before choosing a method: Question Why It Matters How much of the tap is above the surface? Anything protruding gives you more options (weld-out, extractor). Flush or below-surface limits you to EDM, chemical, or milling. Is the tap in one piece or shattered? Shattered taps cannot be extracted with a tap extractor — the claws have nothing solid to grip. EDM or chemical dissolution required. What is the workpiece material? Aluminium opens the chemical dissolution option (the alum trick). Steel, cast iron, and titanium do not. What are the threads worth? If the hole can be drilled out and re-tapped at the next size up, or fitted with a thread insert, that may be faster and cheaper than a careful extraction. What tap size broke? Small taps (M3 and below) are extremely difficult to extract mechanically. EDM is almost always the right answer below M4. Is the hole through or blind? Blind holes trap chips from milling methods. Through holes allow push-through with a punch as a last resort. The Six Methods — Overview Method Best For Not Suitable When Skill Level Tap extractor Clean break above or at surface, tap M6+ Shattered tap, flush/below-surface, small taps Basic Left-hand drill bit Tap protruding slightly, not bottomed out Shattered tap, very small taps, blind holes at bottom Basic Weld-out (TIG/MIG) Tap stub above surface, M6+, steel workpiece Below-surface taps, aluminium workpiece (warps), non-weld environment Intermediate Milling/carbide end mill Tap M6+, access to milling machine or drill press Very small taps, no carbide tooling, blind holes with no clearance Intermediate Chemical dissolution (alum) Tap in aluminium only — any size, any depth Steel, cast iron, titanium, stainless workpiece (dissolves with the tap) Basic — just time EDM / spark erosion Any size, any depth, any workpiece material — the reliable fallback Non-conductive materials (plastics, composites) Machine shop or hire Method 1 — Tap Extractor A tap extractor is a tool with three or four hardened prongs that insert into the flutes of the broken tap. When turned counter-clockwise, the prongs grip the tap and back it out. This is the first method most machinists reach for — and the most commonly misused. When it works The tap broke cleanly — not shattered into fragments The break is at or above the workpiece surface The tap is M6 or larger (prongs need flute clearance) The tap is not bottomed against the end of a blind hole When it fails The tap shattered — no solid section for the prongs to grip The tap is below the surface — prongs can't reach the flutes Small taps (below M4) — flutes are too narrow for the prongs The tap has rolled or welded itself into the hole — no rotational play at all Technique Clear chips from the flutes with compressed air before inserting the extractor. Insert the prongs into the flutes. Seat them fully — a partial engagement will snap the prongs off. Apply gentle counter-clockwise rotation. Do not jerk or force. If it won't move, stop — forcing it will break the extractor prongs into the hole, making the situation far worse. If there is any movement, alternate between half-turns back and quarter-turns forward (as you would with a hand tap) to break the friction gradually. Apply a drop of penetrating oil to the thread before attempting extraction — allow it to soak for 10–15 minutes. Important: Tap extractor prongs are hardened but brittle. Broken prongs in a hole containing a broken tap is a genuinely difficult recovery. If the tap shows no rotational movement after gentle pressure, move to another method. Method 2 — Left-Hand Drill Bit Left-hand (reverse-helix) drill bits cut counter-clockwise. When drilling into a broken tap that is not fully seized, the friction of the drill can grab the tap and wind it out — before the bit even cuts into the tap body. This is a worthwhile first attempt on M6+ taps with some protrusion. The same left-hand drill technique works on broken bolts — see the Bolt Extractor Guide for matched left-hand drill + extractor kits (Bordo per-size, Sutton M603S20L 10pc combined set). Centre-punch the broken tap face as centrally as possible. Select a left-hand drill bit smaller than the tap's minor diameter — you want to drill into the tap, not through the threads. Drill at low speed with firm, steady pressure. Use cutting fluid. The rotation friction often backs the tap out without the drill needing to cut through the full tap body. If the tap does not back out after the drill bites 2–3 mm, the tap is too seized for this method. Do not continue drilling — you risk deflecting off the harder tap body and damaging the surrounding threads. For drill bit substrate selection on hardened tap bodies (cobalt M35/M42 vs solid carbide), see our Cobalt Drill Bit Guide. Method 3 — Weld-Out (TIG or MIG) If the broken tap protrudes by 3 mm or more above the surface, a welder can tack a steel rod, nut, or welding wire to the stub and wind it out with a spanner or pliers. This is highly effective when it can be done — particularly on steel workpieces where surrounding heat distortion is less of a concern. Clean the stub surface of oil and debris. TIG-weld a short length of steel rod (or tack a nut) to the top of the tap stub. MIG can work but TIG gives more control on small stubs. Allow to cool slightly — do not quench. Apply counter-clockwise torque to the welded rod/nut. The weld creates a gripping interface that a tap extractor cannot. If the tap moves, back it out gradually. If not, the weld bond failed — re-weld and try again. Caution on aluminium: Welding near aluminium risks warping thin sections and creating heat-affected zones that damage the base material. The chemical dissolution method (below) is usually the better choice for aluminium. Method 4 — Carbide End Mill / Milling Out A solid carbide end mill can cut through an HSS tap because carbide is significantly harder. This method requires either a milling machine or a drill press with a quality vice and precise setup. It is not a freehand operation. For end mill type, flute count and coating selection (a 4-flute solid carbide TiAlN end mill is the typical choice for this work), see our End Mill Guide. Set the workpiece up precisely on the mill or drill press — the end mill must enter the exact centre of the broken tap. Misalignment by even 0.3 mm on a small tap will cut into the threads. Select a carbide end mill slightly smaller than the tap's minor diameter (the core of the tap, inside the threads). Mill at conservative speed (carbide end mill in HSS tap — reduce normal speed by 30%). Mill in small increments (0.5 mm depth of cut maximum). Use cutting fluid continuously. Once you have removed the bulk of the tap body, the thin flute walls will collapse and can be picked out of the threads with a pick or dental probe. Clean threads with a bottoming tap run by hand before use. The risk with this method is damaging the threads if alignment is off. On critical parts, EDM is a better choice. Method 5 — Chemical Dissolution (The Alum Trick) This method works exclusively on aluminium workpieces. It is the most underrated broken tap removal technique and deserves to be better known. Alum — potassium aluminium sulfate, available at most pharmacies or pool supply stores — dissolves HSS steel (the tap material) in warm acidic solution while leaving aluminium unaffected. The chemistry is straightforward: HSS is iron-based and reacts with the sulphate solution; aluminium forms a protective oxide layer that resists the reaction. Process Fill a non-metallic container (plastic or ceramic) with warm water. Add alum at roughly 50–100 g per litre. The solution does not need to be boiling — warm is sufficient, but warm accelerates the reaction. Submerge the aluminium workpiece fully. If the workpiece is large or cannot be submerged, pack the area around the broken tap with alum paste (alum + small amount of water). Wait. For a small tap (M4–M6) in a crockpot on low heat, expect 2–8 hours. Larger taps or cold-water solutions may take overnight. Remove the workpiece and clear the dissolved tap material from the hole. The threads will be intact. Run a tap through the hole to clean the threads before use. Alternative dissolving agent: Sodium bisulfate (found as pool pH reducer, "pH Down") works similarly to alum. Some machinists prefer it as it is more widely available. What will NOT work: This method does not work on steel, stainless, cast iron, or brass workpieces — the acid will attack the workpiece material as well as the tap. Aluminium only. Method 6 — EDM (Electrical Discharge Machining / Spark Erosion) EDM is the professional-grade solution and the correct choice when: The tap is small (below M4) The tap has shattered into fragments The break is flush with or below the workpiece surface All other methods have been attempted and failed The part is critical and cannot be risked An EDM tap remover uses controlled electrical discharges to erode the tap material without applying mechanical force. The electrode is positioned over the tap and discharges arc between the electrode and the tap, vaporising small amounts of tap material until only the flute shells remain — which can then be removed by hand with a pick. Because the process is non-contact, the surrounding threads are not damaged. This is the only method that reliably removes a shattered tap without destroying the hole. Access options Machine shop service: Most engineering workshops offer EDM tap removal as a service. For a one-off critical part, this is the most cost-effective approach. Portable EDM units: Compact portable EDM tap removers (EDM-8C style) are available to purchase or hire. They handle taps from M2 upward. Suited to workshops that break taps frequently. Tool hire: Portable EDM units are available through industrial tool hire companies in Australia. Limitation: EDM requires the workpiece material to be electrically conductive. It works on steel, aluminium, cast iron, stainless, and titanium — but not on plastics or composites. When to Use a Thread Insert Instead Sometimes the most efficient path is not to remove the tap — it is to accept that the hole is now larger and install a thread repair insert. This is particularly true when: The threads around the broken tap are already damaged from previous extraction attempts The hole can be drilled out and re-tapped to the next standard size with an insert that restores the original thread Speed matters more than original-specification repair Thread repair systems including Recoil (the Australian-made brand) and Helicoil install a hardened stainless steel coil insert into an oversize drilled and tapped hole. For mapping old Recoil part numbers (2007 or 2013 codes) to current RC kit numbers, see our Recoil thread repair cross-reference. The insert provides a new thread at the original size. For example: an M8 thread damaged by a broken tap can be drilled to M10 tap size, tapped M10, and fitted with an M8 Recoil insert that restores the original M8 thread — often stronger than the parent material. For the full reference covering Recoil wire inserts and Keyserts, Helicoil compatibility, TimeSert solid bushings, step-by-step installation, and the steel vs stainless decision, see our Stripped Thread Repair Guide. This approach salvages parts that would otherwise be scrapped and is the standard repair method in automotive, aerospace, and maintenance engineering. Prevention: Why Taps Break Most broken taps are preventable. Understanding the causes eliminates the majority of breakages. Cause Why It Breaks the Tap Prevention Speed too high Heat builds at the cutting edge, tap loses temper and softens Use correct tapping speed (see our Cutting Speeds & Feeds Chart — tapping section) Wrong pilot hole size Tap has too much material to remove — overloaded cutting edge Use correct tap drill size for material and thread form — see our Tap Drill Size Chart No cutting fluid Friction heat, chip welding, tap seizure Always use cutting fluid suited to the material — see our Cutting Fluids Guide Chips packing in blind hole Tap hits chip mass at hole bottom and shears Use a spiral-flute tap for blind holes — see Tap Types Explained Wrong tap type for hole Spiral point (gun tap) in blind hole packs chips; bottoming tap as starter skates sideways Match tap type to hole — taper/plug to start, bottoming to finish blind holes, gun tap for through-holes only Forcing through resistance Tap suddenly harder to turn = chips blocking, side load, or material change. Cranking harder snaps the tap. Stop. Back off, clear chips, re-lubricate, check alignment, then continue gently. Hole not deep enough Tap bottoms out, operator keeps turning, tap shears at the root Drill the hole at least 3 thread pitches deeper than the required tapped depth Prevention beats extraction every time. Stock up on quality taps — before the next one breaks The best broken tap story is the one that never happens. Get the right taps, extractors, and thread repair kits from AIMS Industrial — trusted by Australian tradespeople and maintenance teams nationwide. Taps & extractors Recoil thread repair Talk to a specialist Frequently Asked Questions What causes taps to break? The most common causes are: wrong pilot hole size (too small, overloading the tap), no cutting fluid (friction causes chip welding and tap seizure), chips packing in a blind hole (tap hits the chip mass and shears), tapping speed too high (heat damage to the cutting edge), and the tap bottoming out in a hole that wasn't drilled deep enough. Most broken taps are preventable with the correct setup. Can I drill out a broken tap with a standard HSS drill bit? No. HSS taps are harder than HSS drill bits — a standard twist drill will not cut through a tap. Attempting to drill with an HSS bit will deflect off the tap, damage the surrounding threads, and typically push tap fragments deeper into the hole. Only solid carbide tooling, EDM, or chemical dissolution can remove tap material reliably. What is a tap extractor and when does it work? A tap extractor has hardened prongs that seat in the flutes of a broken tap and apply counter-clockwise torque to back it out. It works when: the tap broke cleanly (not shattered), the break is at or above the surface, the tap is M6 or larger, and the tap has some rotational play. It fails on shattered taps, flush or below-surface breaks, and small taps (below M4). Never force a tap extractor — broken prongs in the hole make the situation significantly worse. What is the alum trick for removing a broken tap from aluminium? Alum (potassium aluminium sulfate) dissolved in warm water dissolves HSS steel taps while leaving aluminium unaffected. Submerge the aluminium workpiece in the alum solution (warm water speeds the reaction) and wait 2–8 hours or overnight depending on tap size. The tap dissolves completely, leaving the threads intact. This method only works in aluminium — do not use it on steel, stainless, cast iron, or brass workpieces. Can I use heat to remove a broken tap? Heat alone rarely removes a broken tap, but it can help in two ways: heating the aluminium workpiece causes the parent material to expand more than the steel tap (different thermal expansion coefficients), which may loosen the tap's grip enough for a tap extractor to work. Second, some machinists anneal the tap by heating to red heat — this softens the HSS, making it possible to drill through with a cobalt bit. However, annealing risks distorting the workpiece and is not recommended for precision parts. What is EDM tap removal? EDM (Electrical Discharge Machining) uses controlled electrical sparks to erode the tap material without applying mechanical force. An electrode is positioned over the tap, and electrical discharges vaporise small amounts of the tap until only the thin flute shells remain — which are then removed by hand. EDM does not damage the surrounding threads. It works on any tap size, any depth, and any workpiece material that is electrically conductive. Machine shops offer it as a service; portable units are also available to purchase or hire. Can I remove a broken tap that is flush with the surface? Yes, but your options are limited. A tap extractor needs the tap to be at or above the surface — flush or below-surface breaks require EDM, carbide milling (on M6+), or chemical dissolution (aluminium only). EDM is the most reliable method for flush and below-surface breaks regardless of tap size. What should I do if the tap has shattered into pieces? EDM is the only reliable method for a shattered tap. Tap extractors cannot grip broken fragments. Mechanical drilling risks embedding fragments further into the threads. EDM erodes all conductive material from the hole — including multiple fragments — without contact. Take the part to a machine shop that offers EDM tap disintegration if you don't have access to an EDM unit. What is a thread insert and when is it the right choice? A thread insert (Recoil, Helicoil) is a hardened stainless steel coil installed in an oversize hole to restore the original thread size. After drilling out the broken tap area and re-tapping to a larger size, the insert provides a new thread at the original specification — often stronger than the parent material. Use this approach when threads are already damaged from extraction attempts, when speed matters more than original-spec repair, or when the damaged hole is in a soft material (aluminium, cast iron) that benefits from a hardened thread. How do I prevent taps from breaking in the future? The main preventions: use the correct tap drill size (too small a pilot hole is the number one cause), always use cutting fluid appropriate for the material, back off every 1–2 turns to break chips in blind holes, drill the hole at least 3 thread pitches deeper than required, and use spiral-flute taps for blind holes. For correct tapping speeds by material, see our Cutting Speeds & Feeds Chart. What is the difference between a spiral-flute tap and a standard tap for blind holes? A standard (hand) tap pushes chips downward into a blind hole. As chips accumulate, the tap meets increasing resistance until it shears. A spiral-flute tap (gun tap for through holes, spiral-flute for blind holes — see our Tap Types Explained guide) curls chips upward and out of the hole, preventing chip packing. For blind holes in any material tougher than aluminium, spiral-flute taps reduce the risk of breakage significantly. Can I remove a tap broken in stainless steel without EDM? It depends on the break. If the tap protrudes and is in one piece, a weld-out or tap extractor may work. Chemical dissolution does not work on stainless. Carbide milling is possible but risks deflecting off the hardened tap body and cutting into the work-hardened stainless threads. EDM is the most reliable choice for stainless — stainless work-hardens rapidly, making mechanical methods less predictable. What size tap extractor do I need? Tap extractors are sized by tap range — typically covering a group of metric sizes (e.g. M3–M4, M5–M6, M8–M10, M12–M14). Match the extractor to the tap size that broke. The prongs must fully seat in the flutes — an oversized extractor will not engage, and an undersized extractor will slip. Tap extractor sets covering M3–M16 are stocked by AIMS and cover the majority of workshop applications. What happens if I break the tap extractor prongs off in the hole? Tap extractor prongs are hardened steel — harder than a drill bit but not as hard as the original tap. You now have multiple pieces of hardened steel in the hole. EDM becomes the only practical solution, and the job is now more complex. This is why forcing a tap extractor is the worst thing you can do — if the tap shows no movement under gentle pressure, stop and switch methods. Is there a method that works on all materials and all situations? EDM is the universal fallback. It works on any tap size (M2 and above), any depth, any break profile (clean, flush, shattered), and any electrically conductive workpiece material. It is the correct choice when other methods have failed or when the part is too critical to risk with mechanical approaches. The only exception is non-conductive workpiece materials (plastics, composites), where mechanical removal or thread insert is required. How long does the alum dissolution method take? With warm water (not boiling) and a crockpot on low heat: a small tap (M4–M5) typically dissolves in 2–4 hours; M6–M8 in 4–8 hours; larger taps may need overnight. Cold water solutions take much longer — 24–48 hours or more. Adding heat significantly accelerates the reaction. Check periodically — once the tap is dissolved, remove the part and rinse thoroughly to stop the reaction. Where can I buy tap extractors and thread repair kits in Australia? AIMS Industrial stocks tap extractor sets (covering M3 through M16), Recoil and Helicoil-compatible thread repair kits, cobalt and solid carbide drill bits for hardened tap material, and the full Sutton Tools Australian-made tap range so the next tap doesn't break. Order online or contact our team for the right tooling for your job. People Also Ask — Broken Tap Removal Q: What is the first step when a tap breaks in a hole? Stop immediately and do not attempt to reverse or force the tap further. Assess whether the broken tap is flush, recessed or protruding, and whether any section is still accessible by hand. Penetrating oil applied around the tap and left to soak can help loosen the tap before any extraction attempt. Q: What tools can remove a broken tap? Common options include tap extractors (finger-type tools that grip the flutes), EDM (electrical discharge machining) which erodes the tap without touching the workpiece, carbide drill-out if the tap material is softer than the surrounding workpiece, and chemical dissolution in aluminium workpieces where nitric acid dissolves steel taps. The best method depends on tap size, workpiece material and how firmly the tap is stuck. Q: Can I drill out a broken HSS tap? Drilling out a broken HSS tap is extremely difficult because HSS is hardened. A carbide drill is required, and even then the tap's hard flutes tend to deflect the drill. EDM is generally the preferred method for removing broken HSS taps cleanly, particularly in precision workpieces where damaging the hole wall is not acceptable. Q: How can I prevent taps from breaking in the first place? Use the correct tap drill size for the thread and material, apply cutting fluid consistently, clear chips frequently by reversing half a turn during tapping, avoid forcing the tap when resistance increases, and use spiral-flute or spiral-point taps in materials prone to chip packing such as aluminium and stainless steel.
Read more
Cutting Fluids & Cutting Oils: Types, Selection & Applications Guide
This guide is part of AIMS Industrial's curated Engineering Reference Charts library — 78 reference articles across fasteners, threading, bearings, lubrication and safety standards. What Is Cutting Fluid and Why Does It Matter? Cutting fluid is any liquid applied at the cutting zone during machining, drilling, tapping, milling, or sawing operations. It serves two distinct functions that are impossible to separate in practice: lubrication and heat removal. When a drill bit or cutting tool removes material, it generates heat through friction and the deformation of the workpiece material. That heat does several things — it softens the cutting edge, accelerates tool wear, causes the workpiece to expand (affecting dimensional accuracy), and can cause built-up edge (BUE) on the tool, where workpiece material welds to the cutting edge and dramatically increases cutting forces. Cutting fluid attacks all of these problems simultaneously. Beyond cooling and lubrication, cutting fluids also flush away chips and swarf from the cutting zone. Chips left in a drill hole or milling slot act as an abrasive — recutting the swarf accelerates tool wear and can cause the tool to bind or break. A flood of cutting fluid carries chips out of the cut. The practical result of using the right cutting fluid: tools last longer, surface finish improves, dimensional accuracy is easier to maintain, and taps are significantly less likely to break. For AIMS customers regularly drilling, tapping, and machining steel, aluminium, and stainless, cutting fluid is not optional — it is a standard part of the operation. Types of Cutting Fluid: An Overview Cutting fluids fall into four broad categories. Understanding the differences helps you select the correct product for each operation and material, rather than defaulting to whatever is on the shelf. Neat Cutting Oil Neat cutting oil is an undiluted petroleum or mineral oil, sometimes with extreme-pressure (EP) additives such as sulphur, chlorine, or phosphorus compounds. It is used straight from the container — it is not diluted with water. Neat oils provide excellent lubrication and are particularly suited to heavy-duty operations such as gear hobbing, broaching, threading, and operations on difficult-to-machine materials like stainless steel and high-temperature alloys. The trade-off: neat oils have poor cooling ability compared to water-based fluids. They are also more expensive per litre, produce smoke at elevated temperatures, and require care around fire risk in high-speed operations. For low-speed, high-load operations where lubrication is paramount, neat oil is the right choice. Note — Important for aluminium: Some neat cutting oils contain active sulphur additives. Active sulphur reacts with aluminium and copper alloys, causing staining and surface discolouration. Always check that a neat cutting oil is rated for non-ferrous use before applying it to aluminium, brass, or copper. Many sulphur-based oils are explicitly marked "for ferrous metals only." Soluble (Water-Miscible) Cutting Oil Soluble cutting oil, also called soluble oil or emulsifiable oil, is a concentrate that is mixed with water before use. When mixed, the oil forms a stable emulsion — a milky-white fluid containing oil droplets suspended in water. The water phase provides cooling; the oil phase provides lubrication. Soluble oils are the most widely used cutting fluids in general machining and are the standard choice for most workshop operations: drilling, milling, turning, and grinding. They are economical (a 20-litre concentrate produces hundreds of litres of working fluid), easy to use, and provide a good balance of cooling and lubrication for the majority of engineering materials. Common AU examples: Penrite Soluble Oil, Fuchs XDP 1800, Castrol Hysol. These products are all emulsifiable concentrates and work on the same principle. Semi-Synthetic Cutting Fluid Semi-synthetics are a hybrid — a water-dilutable concentrate containing both oil and synthetic chemical lubricants. They produce a translucent or clear fluid rather than the milky emulsion of a soluble oil. Semi-synthetics offer improved biological stability (they resist bacterial growth longer than soluble oils), better cooling, and improved visibility of the cutting zone. They are the preferred choice in many CNC machining centres for these reasons. Semi-synthetics do cost more than basic soluble oils. Synthetic Cutting Fluid True synthetics contain no petroleum oil — they are entirely water-based solutions of chemical compounds (amines, glycols, corrosion inhibitors, biocides). They offer the best cooling performance, excellent corrosion protection, and the longest sump life of any cutting fluid type. Synthetics are used in high-speed grinding and some CNC operations. They provide no oil-film lubrication, which limits their use for tapping and threading where high lubrication is needed. Paste and Gel Cutting Compounds Cutting pastes (such as Trefolex CT) are dense, waxy compounds applied directly to taps, dies, and drill bits before the cut. They are not flood coolants — they provide concentrated lubrication at the cutting edge without dripping. Cutting paste is the standard choice for manual tapping, hand die cutting, and hole sawing operations where applying liquid coolant is impractical. Trefolex is the most widely recognised brand in Australia for this application. Cutting Fluid Selection by Material Matching the fluid to the workpiece material is as important as matching it to the operation. The following guide covers the most common materials encountered in Australian workshops and field applications. Mild Steel and Carbon Steel General purpose soluble cutting oil (mixed per the manufacturer's concentration recommendation, typically 1:20 to 1:30) is the correct fluid for most steel drilling, milling, and turning. For heavy-duty operations — deep-hole drilling, form tapping, gear cutting — use neat cutting oil with EP additives. Cutting paste is appropriate for manual tapping in steel. Stainless Steel Stainless steel is one of the most demanding materials for cutting fluids. It work-hardens rapidly, meaning a blunt tool or poor lubrication causes the surface to harden ahead of the cutting edge — the tool then struggles to cut the hardened layer and may break or rub without cutting. Use a neat cutting oil or EP-rated soluble oil specifically formulated for stainless, applied generously. Slow speeds and high feed rates also help prevent work-hardening. Do not use ordinary domestic cutting oil on stainless — use an EP-rated product. Aluminium and Aluminium Alloys Aluminium machining has two specific challenges. First, aluminium is soft and sticky — it tends to build up on cutting edges (BUE), causing poor surface finish and tool loading. Second, sulphur-based cutting oils stain aluminium. For aluminium, use: A dedicated aluminium cutting fluid (many are kerosene-based or use synthetic lubricity additives without active sulphur) Tap Magic Aluminium (purpose-formulated) WD-40 for light-duty or occasional use — it is acceptable for aluminium drilling and tapping in a workshop context Paraffin/kerosene for manual operations Avoid sulphur-bearing neat cutting oils on aluminium — they cause brown or black staining of the machined surface. Cast Iron Cast iron is typically machined dry. The graphite content of cast iron acts as a self-lubricant and the cutting dust does not form a built-up edge. Using cutting fluid on cast iron creates a black slurry of cast iron dust that clogs the fluid sump and is difficult to filter. Machine cast iron dry where possible. Copper, Brass, and Bronze Copper alloys machine well with light mineral oil or kerosene. Avoid sulphur-bearing oils — active sulphur stains copper alloys yellow/brown. Dedicated non-ferrous cutting oils are the safest choice. WD-40 is acceptable for light operations on brass. Titanium and High-Temperature Alloys These materials require aggressive flood cooling — a large volume of soluble oil or semi-synthetic applied directly to the cutting zone. High-pressure coolant systems are used in CNC environments. For workshop operations, heavy EP neat oil with maximum lubrication is preferred for any tapping or threading in titanium. These materials are unforgiving — use cutting fluid without exception. Cutting Fluid Selection by Operation Drilling Use soluble cutting oil (diluted) for general drilling in steel. Cutting paste or neat oil for deep-hole drilling. WD-40 is an acceptable field substitute for small-diameter holes in mild steel or aluminium when nothing else is available, but it evaporates quickly and provides minimal cooling for continuous operations. Tapping and Threading Tapping is the highest-risk operation for breakage, and cutting fluid is critical. Use cutting paste (Trefolex, Tap Magic) for hand tapping — apply it to the tap before each hole. For machine tapping on a CNC or tapping head, use neat cutting oil or an EP-rated soluble oil for steel; dedicated aluminium tapping fluid for aluminium. Broken taps are expensive — the right fluid is cheap insurance. Milling Flood coolant (soluble oil) is standard for CNC and power milling operations. For manual milling on a knee mill or bridgeport, soluble oil in a drip or mist system. For interrupted cuts in aluminium (peripheral milling), some machinists prefer cutting dry or with air blast to avoid thermal shock cracking of the carbide insert — seek advice for specific inserts. Turning (Lathe) Flood coolant (soluble oil) is standard on lathes. For hobby lathes without a coolant system, use cutting paste or a brush-applied neat cutting oil for each pass. Cast iron is machined dry on the lathe as with other operations. For the RPM and surface speed side of lathe work — formula, cutting speeds by material, CSS vs G97 and chuck speed limits — see our Lathe RPM Formula Guide. Sawing (Bandsaw and Hacksaw) Bandsaw cutting of steel benefits significantly from a mist or drip cutting fluid system — it extends blade life dramatically. Cutting paste applied to the blade is an acceptable alternative for reciprocating hacksaws. Cold saw cutting (circular cold saws) typically uses neat cutting oil. Grinding Grinding uses specialised water-based grinding fluids — these are not the same as cutting oils. Grinding coolants prioritise cooling (the grinding wheel generates substantial heat) and chip (swarf) flushing. Do not use neat cutting oil in a grinding application. Soluble Oil: Mixing Ratios Explained Soluble cutting oil concentrates must be mixed with water before use. Getting the concentration right matters — too dilute and you lose lubrication performance; too concentrated and you waste expensive concentrate and may cause foaming or skin issues. Typical recommended concentrations: Operation Typical Ratio (Concentrate : Water) Approx % Concentrate General machining (drilling, milling, turning) 1:20 to 1:30 3–5% Heavy-duty machining, difficult materials 1:10 to 1:20 5–10% Grinding 1:40 to 1:60 1.5–2.5% Always add concentrate to water — not water to concentrate. Adding water to concentrate can cause the emulsion to invert and not mix correctly. Mix by adding the concentrate slowly while stirring, or use a hand refractometer (a simple optical tool) to verify concentration. A refractometer reads the refractive index of the emulsion and converts it to concentration — they cost around $30–50 and remove the guesswork entirely for shops that mix cutting fluid regularly. Check the manufacturer's data sheet for the specific product — ratios vary between products and concentration recommendations differ for different materials. Common Substitutes: What Works and What Doesn't WD-40 WD-40 is widely used as a cutting fluid substitute in workshops, particularly for aluminium. It contains light mineral spirits and provides reasonable lubrication for light drilling and tapping in aluminium and mild steel. It evaporates quickly, so it is not suitable for sustained or high-speed operations. It is not a replacement for EP cutting oil on stainless or for heavy tapping. But for occasional use when you don't have the right fluid on hand, WD-40 is a legitimate field option for aluminium — it has no sulphur and won't stain. Engine Oil or Machine Oil Used engine oil and lubricating oils are not cutting fluids. They provide some lubrication but have no EP additives, minimal cooling ability, and contain combustion contaminants (used engine oil). In a genuine emergency for one-off light cuts, machine oil will work better than nothing. For regular use, use a proper cutting fluid — the cost difference between a proper product and a compromised result is not worth the saving. Kerosene / Paraffin Kerosene is a legitimate cutting fluid for aluminium and was commonly used before purpose-formulated products became widely available. It prevents BUE on aluminium effectively and has no sulphur. It is still used by some hobbyists and machinists for aluminium tapping. Fire hazard is a consideration in enclosed spaces — ensure adequate ventilation. Brands Stocked in Australia Several cutting fluid brands are well-established in the Australian market: Trefolex CT: The best-known cutting paste in Australia. A dense, waxy compound supplied in a tin. Used for hand tapping, die cutting, and hole saws. Suitable for steel, stainless, and aluminium (it does not contain active sulphur). Tap Magic: A US-origin brand with multiple formulations — Tap Magic Aluminium (kerosene-based, non-staining), Tap Magic Steel, Tap Magic Stainless. Available in aerosol and liquid forms. Popular in Australian workshops for hand tapping and drilling. Fuchs XDP 1800: A semi-synthetic water-soluble cutting fluid used in machine shops and manufacturing. Diluted with water for use in flood coolant systems. Penrite Soluble Oil: A mineral oil-based emulsifiable concentrate for general machining. Health, Safety, and Disposal Skin Contact Prolonged or repeated skin contact with cutting fluids — particularly soluble oils — can cause dermatitis and skin irritation. Wear appropriate nitrile gloves for prolonged machine operation. Wash hands thoroughly after contact. Mist systems generate airborne droplets which can be inhaled — ensure adequate workshop ventilation or use respiratory protection where mist is generated. Cutting Fluid Sump Maintenance Soluble oil sumps support bacterial and fungal growth over time, particularly if the concentration falls below the recommended level or if the sump is not turned over regularly. Signs of biological contamination: a rotten egg or sour smell, brown/grey discolouration, or a "Monday morning smell" from the sump. Treat with a biocide additive. Drain and clean the sump at regular intervals (typically every 3–6 months depending on usage). Do not top up a contaminated sump with fresh concentrate — it will not rescue a biologically compromised fluid. Disposal Used cutting fluid (particularly soluble oil emulsions) cannot be poured down the drain — it is a regulated trade waste in Australia. Options for disposal: Contact your local council or waste management provider for used coolant disposal — many industrial waste services collect in bulk Crack the emulsion using acidification or salt addition, separate the oil phase, and dispose of each phase appropriately Small quantities (home workshop) can often be disposed of at council hazardous waste drop-off days Neat cutting oils are classed as waste mineral oil and must be collected by a licensed waste oil recycler. Cutting Fluid Selection Quick Reference Material Light Duty (Drilling/Tapping) Heavy Duty (Threading/Broaching) Mild / carbon steel Soluble oil (1:20) Neat cutting oil (EP) Stainless steel EP soluble oil or neat EP oil Neat cutting oil (EP, high sulphur) Aluminium Tap Magic Aluminium / WD-40 / kerosene Dedicated aluminium cutting oil (sulphur-free) Cast iron Dry Dry Brass / copper Light mineral oil / kerosene Non-ferrous neat oil (sulphur-free) Titanium EP neat oil (heavy) EP neat oil (heavy), high flood volume Keep your tools cutting longer. Shop cutting fluids & oils — neat, soluble & synthetic stocked From neat cutting oils for heavy turning to soluble coolants for milling and tapping fluids for threading — AIMS Industrial stocks cutting lubricants for steel, aluminium, stainless and more, ready to ship Australia-wide. Browse cutting fluids Tap Magic FAQ Talk to a specialist Frequently Asked Questions What is the difference between cutting fluid and cutting oil? The terms are often used interchangeably, but cutting oil technically refers to neat (undiluted) oil-based products, while cutting fluid is the broader category covering neat oils, soluble oil emulsions, semi-synthetics, and synthetics. In everyday use, "cutting oil" and "cutting fluid" mean the same thing to most tradespeople — any product applied at the cutting zone to lubricate and cool. Can I use WD-40 as a cutting fluid? Yes, with caveats. WD-40 is an acceptable substitute for light drilling and tapping in aluminium and mild steel. It contains light mineral spirits, has no active sulphur, and won't stain aluminium. It is not suitable for sustained high-speed operations (it evaporates too quickly), heavy tapping in steel, or any work in stainless steel where EP lubrication is needed. Use a proper cutting fluid for regular production work. What is soluble cutting oil and what ratio do I mix it? Soluble cutting oil is an oil concentrate that forms a milky white emulsion when mixed with water. For general machining (drilling, milling, turning), mix at approximately 1 part concentrate to 20–30 parts water (3–5% concentrate). For heavier operations, increase to 1:10 (10%). Always add concentrate to water, not the other way around. Use a refractometer to verify concentration accurately. What cutting fluid should I use for aluminium? Use Tap Magic Aluminium, a dedicated aluminium cutting oil (sulphur-free), kerosene/paraffin, or WD-40. Avoid sulphur-bearing cutting oils on aluminium — active sulphur causes brown or black staining of the machined surface. The staining is surface-only but looks poor and can affect anodising if the part is to be further finished. What cutting fluid should I use for stainless steel? Use an EP (extreme pressure) rated neat cutting oil or an EP-rated soluble oil specifically recommended for stainless. Stainless work-hardens rapidly — poor lubrication allows the surface to harden ahead of the cut, which can shatter taps and ruin tools. Apply generously and use slower speeds than you would for mild steel. Can I use engine oil as cutting fluid? In a genuine emergency, yes — it is better than nothing for a light cut. Engine oil provides some lubrication but has no EP additives, poor cooling, and (if used) may contain combustion contaminants that contaminate the workpiece surface. For regular machining use a proper cutting fluid. The cost of purpose-formulated cutting fluid is negligible compared to broken taps and poor surface finish. What is tapping fluid? Is it different from cutting fluid? Tapping fluid is simply cutting fluid marketed specifically for tapping and threading operations. Most tapping fluids are neat cutting oils or cutting pastes with EP additives — they prioritise lubrication over cooling, which is correct for the low-speed, high-pressure conditions of tapping. Trefolex CT paste and Tap Magic are both tapping fluids. They can also be used for drilling, broaching, and other cutting operations. What is neat cutting oil vs soluble cutting oil? Neat cutting oil is used undiluted, straight from the container. It is an oil product and does not mix with water. Soluble (water-miscible) cutting oil is a concentrate designed to be diluted with water, forming an oil-in-water emulsion. Neat oils provide superior lubrication; soluble oils provide better cooling. Use neat oil for low-speed, heavy-duty operations (tapping, threading, broaching). Use soluble oil for general drilling, milling, and turning where both cooling and lubrication are needed. Does cutting fluid really extend tool life? Significantly, yes. Tool failure in machining operations is predominantly thermal — heat softens the cutting edge and accelerates wear. Studies in machining show that cutting fluid can extend tool life by 50–300% depending on the material and operation. For taps specifically, the difference between dry and properly lubricated tapping in steel is the difference between a tap lasting dozens of holes or breaking on the first. Cutting fluid is never optional in production work. Do I need cutting fluid for drilling mild steel at home? For occasional drilling with HSS bits in mild steel, you can get away without it for small holes at slow feed rates — HSS tolerates moderate heat. But adding cutting fluid (even WD-40) improves the result noticeably: cleaner cut, longer bit life, no bluing (heat discolouration) on the steel. For holes larger than about 10mm, stainless steel, or when drilling into existing structures where bit replacement is inconvenient, use cutting fluid without question. How do I dispose of used cutting fluid? Used cutting fluid (particularly soluble oil emulsions) cannot be poured down the sink or stormwater drains in Australia — it is regulated trade waste. Contact your local council hazardous waste service for small workshop quantities. Industrial users should engage a licensed waste oil recycler or trade waste contractor. Neat cutting oils are collected with used lubricating oil by licensed waste oil recyclers. What concentration is my soluble oil at? How do I check? Use a hand refractometer — a small optical instrument available for $30–50 from industrial suppliers. Fill the prism with a drop of your cutting fluid and read the scale — it shows Brix or refractive index, which you convert to concentration using the factor provided by the cutting fluid manufacturer (typically 1.0–1.5). Check concentration weekly in active sumps and top up with concentrate if it falls below the recommended minimum. Why does my cutting fluid smell bad? A rotten egg or sour smell from soluble oil cutting fluid indicates bacterial contamination of the sump. Bacteria thrive in cutting fluid sumps, particularly at dilute concentrations (below 3%), warm temperatures, or where the sump is not agitated regularly. Treat with a biocide additive, raise the concentration to the recommended level, and clean the sump. A heavily contaminated sump should be drained, cleaned, and refilled — do not continue using biologically contaminated fluid. Our Tap Types guide covers every cutting and forming tap variant with material-specific selection rules. People Also Ask — Cutting Fluids & Coolants Q: What does cutting fluid actually do? Cutting fluid does three jobs at once: it cools the tool and workpiece, it lubricates the cutting action to reduce friction and built-up edge, and it flushes chips and swarf away from the cut. Cooling protects tool hardness and keeps the workpiece dimensionally stable; lubrication improves surface finish and extends tool life; chip flushing stops swarf re-cutting and damaging the finish. Some operations lean more on cooling (high-speed turning), others more on lubrication (tapping and threading). Matching the fluid and how it is delivered to the operation is what keeps tools lasting longer and finishes cleaner. Q: What are the main types of cutting fluid? There are four broad families. Straight (neat) cutting oils are not mixed with water and give the best lubrication, suiting heavy, low-speed operations like tapping and broaching. Soluble (emulsion) oils mix with water to form a milky fluid that balances cooling and lubrication for general machining. Semi-synthetic fluids carry less oil and run cleaner with good cooling. Full synthetic fluids contain no mineral oil, give the strongest cooling and the cleanest sumps, and suit high-speed grinding and machining. As a rule, the more lubrication-dependent and slower the cut, the more you lean toward oils; the more cooling-dependent and faster the cut, the more you lean toward synthetics. Q: Should I use neat oil or a water-soluble coolant? It comes down to whether the operation needs lubrication or cooling most. Neat cutting oils win where lubrication and surface finish dominate and heat is modest — heavy tapping, threading, gun-drilling and broaching. Water-soluble coolants win where heat removal dominates — higher-speed turning, milling and grinding — because water carries heat away far better than oil. Soluble and synthetic coolants are also generally cleaner to work around and cost less per litre in use once diluted. If an operation generates a lot of heat, lean to a water-mix coolant; if it is slow and heavily loaded, lean to a neat oil. Q: How do I mix and maintain a water-soluble coolant? Always add the concentrate to the water, not water to the concentrate, so the emulsion forms correctly and stays stable. Mix to the dilution the manufacturer specifies for your operation and check it regularly with a refractometer, topping up with correctly mixed fluid rather than plain water as the sump evaporates. Keep the sump clean of tramp oil and swarf, keep it aerated, and watch for souring (a bad smell) which signals bacterial growth and a coolant due for change. Well-maintained coolant lasts longer, protects the machine from corrosion and gives consistent tool life — neglected coolant does the opposite. Q: Can one cutting fluid be used for all metals? A good general-purpose soluble or semi-synthetic coolant will cover a wide range of steel and cast-iron machining, but a single fluid is rarely ideal for everything. Some metals have specific needs — for example, certain fluids and additives can stain or react with aluminium, copper and their alloys, so a compatible fluid should be confirmed for those. Heavy operations like tapping stainless often benefit from a dedicated high-lubricity oil or paste. The practical approach is to run a versatile coolant for the bulk of your work and keep a specialist fluid on hand for the demanding or reactive jobs. Tell us your materials and operations and we can match products. For long drill bits, see our long drill bits range stocked across Australia.
Read more
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.
Read more
Tap Drill Size Chart: Metric & Imperial Thread Sizes
Tap drill size is the diameter of the pilot hole drilled before threading. The rule: drill diameter = thread outer diameter − thread pitch. For M8 × 1.25 coarse, the tap drill is 6.8mm. For 1/4" BSP, it's 11.8mm. The compact reference below covers the most-used metric coarse sizes; full metric fine, BSP, UNC and UNF charts are further down. (If you are looking for the Sutton Tap & Drill Chart PDF, click here.) Quick answer — most common sizes Metric coarse: M3 = 2.5mm · M4 = 3.3mm · M5 = 4.2mm · M6 = 5.0mm · M8 = 6.8mm · M10 = 8.5mm · M12 = 10.2mm · M14 = 12.0mm · M16 = 14.0mm · M20 = 17.5mm BSP: 1/8" = 8.8mm · 1/4" = 11.8mm · 3/8" = 15.0mm · 1/2" = 18.6mm UNC: 1/4"-20 = 5.1mm · 5/16"-18 = 6.9mm · 3/8"-16 = 7.9mm · 1/2"-13 = 10.7mm Formula: tap drill (mm) = thread OD − pitch. Full charts below. For more engineering reference charts and selection tables, see our Engineering Reference Charts hub — covering fasteners, bearings, lubrication, measuring, welding and Australian standards. Tap & Drill Bit Selector — Most-Asked Metric Sizes This page is a working selector tool — not just a reference. Use it to get the right tap and drill into your hand in one click. The 10 most-asked metric thread sizes at AIMS are below. For less common sizes, scroll to the full charts further down (use the jump-nav below). How to use: 1. Find your thread size 2. See the matching tap drill diameter 3. Click Buy Tap or Buy Drill — sized to match M3 Tap drill 2.5 mm Buy tap → Buy drill → M4 Tap drill 3.3 mm Buy tap → Buy drill → M5 Tap drill 4.2 mm Buy tap → Buy drill → M6 Tap drill 5.0 mm Buy tap → Buy drill → M8 Tap drill 6.8 mm Buy tap → Buy drill → M10 Tap drill 8.5 mm Buy tap → Buy drill → M12 Tap drill 10.2 mm Buy tap → Buy drill → M14 Tap drill 12.0 mm Buy tap → Buy drill → M16 Tap drill 14.0 mm Buy tap → Buy drill → M20 Tap drill 17.5 mm Buy tap → Buy drill → Default recommendation: Sutton Spiral Point HSS taps and Sutton D101 Silver Bullet HSS jobber drills — the workshop standard for mild steel. AIMS also stocks Bordo and P&N as alternates. For stainless steel or hardened steel, switch to cobalt drill bits + cobalt taps (see the "By Material" section below). Need help? Call us on (02) 9773 0122. Jump to: Metric Coarse Metric Fine BSP UNC UNF By Material Related Selectors Tap Drill Size Chart — Metric Coarse Quick Reference The most frequently used metric coarse thread sizes and their tap drill diameters: Thread Tap Drill (mm) Thread Tap Drill (mm) M3 2.5 M12 10.2 M4 3.3 M14 12.0 M5 4.2 M16 14.0 M6 5.0 M18 15.5 M8 6.8 M20 17.5 M10 8.5 M24 21.0 How to Use This Chart Tap drill size refers to the diameter of the hole you drill before running a tap through it. The hole must be smaller than the thread's outer diameter, leaving enough material for the tap to cut the thread profile. Too large and the thread is shallow and weak. Too small and you risk breaking the tap. As a general rule, tap drill size = thread outer diameter − thread pitch. This gives approximately 75% thread engagement, which is standard for most applications. For softer materials or where tap breakage is a concern, go slightly larger. For maximum thread strength in hard materials, go slightly smaller. By accurately matching the tap size to the drill size and choosing the right tap for the job, you can achieve optimal results in your thread cutting operations. Metric Coarse Tap Drill Size Chart Metric coarse is the standard thread series for most bolts, screws and tapped holes in general engineering. Pitch is expressed in millimetres — a lower number means finer threads. These are the sizes you'll use for the vast majority of metric tapping work. Need help finding your size? Call AIMS on (02) 9773 0122 — the team can confirm stock and pick the right tap type for your job. Or browse all metric coarse taps and jobber drill bits. Thread Size Pitch (mm) Tap Drill (mm) Tap Drill (inch approx.) M1 0.25 0.75 --- M1.2 0.25 0.95 --- M1.4 0.30 1.10 --- M1.6 0.35 1.25 --- M1.8 0.35 1.45 --- M2 0.40 1.60 1/16" M2.5 0.45 2.05 5/64" M3 0.50 2.50 3/32" M3.5 0.60 2.90 7/64" M4 0.70 3.30 1/8" M5 0.80 4.20 11/64" M6 1.00 5.00 13/64" M7 1.00 6.00 15/64" M8 1.25 6.80 17/64" M10 1.50 8.50 21/64" M12 1.75 10.20 25/64" M14 2.00 12.00 15/32" M16 2.00 14.00 35/64" M18 2.50 15.50 39/64" M20 2.50 17.50 11/16" M22 2.50 19.50 49/64" M24 3.00 21.00 53/64" M27 3.00 24.00 15/16" M30 3.50 26.50 1-3/64" M33 3.50 29.50 1-5/32" M36 4.00 32.00 1-17/64" M39 4.00 35.00 1-3/8" M42 4.50 37.50 1-15/32" M45 4.50 40.50 1-19/32" M48 5.00 43.00 1-11/16" Metric Fine Tap Drill Size Chart Metric fine threads are used where vibration resistance, fine adjustment, or higher tensile strength is required — common in automotive, aerospace, and precision engineering applications. Multiple pitches exist per diameter; confirm your pitch before selecting the drill. Need help finding your size? Call AIMS on (02) 9773 0122 — the team can confirm stock and pick the right tap type for your job. Or browse all metric fine taps and jobber drill bits. Thread Size Pitch (mm) Tap Drill (mm) M1 × 0.2 0.20 0.80 M1.2 × 0.2 0.20 1.00 M1.4 × 0.2 0.20 1.20 M1.6 × 0.2 0.20 1.40 M2 × 0.25 0.25 1.75 M2.5 × 0.35 0.35 2.15 M3 × 0.35 0.35 2.65 M3.5 × 0.35 0.35 3.15 M4 × 0.5 0.50 3.50 M5 × 0.5 0.50 4.50 M6 × 0.75 0.75 5.25 M7 × 0.75 0.75 6.25 M8 × 0.75 0.75 7.25 M8 × 1.0 1.00 7.00 M10 × 0.75 0.75 9.25 M10 × 1.0 1.00 9.00 M10 × 1.25 1.25 8.75 M12 × 1.0 1.00 11.00 M12 × 1.25 1.25 10.75 M12 × 1.5 1.50 10.50 M14 × 1.0 1.00 13.00 M14 × 1.25 1.25 12.75 M14 × 1.5 1.50 12.50 M16 × 1.0 1.00 15.00 M16 × 1.5 1.50 14.50 M18 × 1.5 1.50 16.50 M18 × 2.0 2.00 16.00 M20 × 1.5 1.50 18.50 M20 × 2.0 2.00 18.00 M22 × 1.5 1.50 20.50 M22 × 2.0 2.00 20.00 M24 × 1.5 1.50 22.50 M24 × 2.0 2.00 22.00 M27 × 2.0 2.00 25.00 M30 × 1.5 1.50 28.50 M30 × 2.0 2.00 28.00 M33 × 2.0 2.00 31.00 M36 × 1.5 1.50 34.50 M36 × 3.0 3.00 33.00 Tap & Drill Selection by Material The right tap drill diameter is one half of the job. The other half is choosing tap and drill geometry that match your workpiece material. This is where most beginner tappers come unstuck — wrong tap type for the material means broken taps, oversized threads, or torn surface finishes. Here's what the AIMS workshop crew reaches for, by material: Mild steel (most common workshop material) Drill: Sutton D101 Silver Bullet HSS jobber (bright finish, 118° point) for occasional tapping. Sutton D102 Blue Bullet HSS (steam-oxide finish) for production tapping — the steam oxide finish helps swarf release on steel. Tap: Sutton Spiral Point HSS taps (T1xx series) for through holes — fastest, swarf pushes ahead of the tap. For blind holes, switch to Spiral Flute (T2xx series) so swarf evacuates upward and out of the hole. Lubricant: Tap Magic Original or any general-purpose cutting fluid. Stainless steel (304, 316, 17-4 PH) Drill: Cobalt drill bit — Sutton D108 or D109 cobalt jobber. The 5% to 8% cobalt content lets the drill stay sharp through stainless's work-hardening tendency. HSS bright drills will glaze the hole surface, work-harden the steel, and snap on the next pass. Tap: Cobalt steel tap — Sutton Spiral Flute Premium HSS Cobalt or Sutton Premium HSS Tinite-coated. The cobalt grade survives the harder material; cheap HSS chrome taps will snap on the first thread. Lubricant: Tap Magic for Stainless Steel — specifically formulated. Don't skimp here. Aluminium, brass, copper, plastics Drill: Standard HSS Sutton D101 Silver Bullet is fine. Some users prefer a slightly higher helix angle drill for softer non-ferrous materials — Sutton's 130° or 140° point geometry options. Tap: Spiral Flute tap is excellent here — long stringy chips need to evacuate cleanly, and spiral flute pulls them up and out. Avoid spiral point in soft aluminium (it bunches chips inside the hole). Lubricant: Tap Magic Aluminium variant — formulated to prevent the gummy build-up that aluminium causes on standard cutting fluids. Cast iron (grey, ductile, malleable) Drill: HSS Sutton D102 Blue Bullet (steam-oxide). Cast iron is brittle and abrasive — the steam oxide finish helps prolong drill life. Tap: Straight Flute tap (T4xx series) or hand tap. Cast iron breaks into powder rather than chips, so spiral evacuation isn't needed — straight flute is more rigid and handles the abrasiveness better. Lubricant: Generally tapped DRY — no cutting fluid needed for cast iron because chips are powder, not strings. 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 drilling. Solid carbide drills + thread mills are the right answer here, not standard taps. Contact us or call (02) 9773 0122 — we'll save you broken taps and damaged workpieces. The AIMS workshop rule: The right cutting fluid is worth more than the right tap. Even a premium Sutton tap will fail prematurely if you're tapping stainless without proper lubrication. Tap Magic cutting fluid guide covers which formulation matches your material. BSP Tap Drill Size Chart (British Standard Pipe) BSP threads are used on pipe fittings, hydraulic connections, and pneumatic systems throughout Australia and the UK. Sizes refer to the nominal bore of the pipe — not the actual thread diameter, which is always larger. BSPP (parallel) and BSPT (taper) share the same thread form and the same tap drill size. Need help finding your size? Call AIMS on (02) 9773 0122 — the team can confirm stock and pick the right tap type for your job. Or browse all BSP taps and jobber drill bits. Nominal Size TPI Tap Drill (mm) Tap Drill (inch) 1/16" BSP 28 6.6 0.261" 1/8" BSP 28 8.8 0.347" 1/4" BSP 19 11.8 0.465" 3/8" BSP 19 15.0 0.590" 1/2" BSP 14 18.6 0.733" 3/4" BSP 14 24.3 0.956" 1" BSP 11 30.5 1.200" 1¼" BSP 11 39.2 1.544" 1½" BSP 11 45.1 1.776" 2" BSP 11 57.0 2.245" 2½" BSP 11 72.6 2.858" 3" BSP 11 87.8 3.457" The 1/4" BSP tap drill size (11.8mm) is one of the most commonly referenced in Australian trade and industrial work. If you're unsure whether your fitting is BSPP or BSPT, the tap drill size is the same for both — the distinction only matters when selecting the tap itself. UNC Tap Drill Size Chart (Unified National Coarse) UNC is the standard US coarse thread series. Common in imported machinery, agricultural equipment, and items manufactured to American standards. Identified by thread count in threads per inch (TPI). Need help finding your size? Call AIMS on (02) 9773 0122 — the team can confirm stock and pick the right tap type for your job. Or browse all UNC taps and jobber drill bits. Thread TPI Tap Drill (mm) Tap Drill (fractional inch) #4-40 40 2.4 3/32" #5-40 40 2.65 --- #6-32 32 2.8 7/64" #8-32 32 3.5 9/64" #10-24 24 3.9 5/32" 1/4"-20 20 5.1 13/64" 5/16"-18 18 6.9 17/64" 3/8"-16 16 7.9 5/16" 7/16"-14 14 9.4 3/8" 1/2"-13 13 10.7 27/64" 9/16"-12 12 12.3 31/64" 5/8"-11 11 13.5 17/32" 3/4"-10 10 16.7 21/32" 7/8"-9 9 19.4 49/64" 1"-8 8 22.2 7/8" 1-1/8"-7 7 25.4 1" 1-1/4"-7 7 28.6 1-1/8" 1-3/8"-6 6 31.0 1-7/32" 1-1/2"-6 6 34.1 1-11/32" UNF Tap Drill Size Chart (Unified National Fine) UNF has a finer pitch than UNC — more threads per inch, higher tensile strength, and better vibration resistance. Used in aerospace, precision equipment, and anywhere a finer thread is specified. When in doubt, check the thread count: more threads per inch means UNF. Need help finding your size? Call AIMS on (02) 9773 0122 — the team can confirm stock and pick the right tap type for your job. Or browse all UNF taps and jobber drill bits. Thread TPI Tap Drill (mm) Tap Drill (fractional inch) #4-48 48 2.3 3/32" #6-40 40 2.9 7/64" #8-36 36 3.5 9/64" #10-32 32 3.8 9/64" 1/4"-28 28 5.6 7/32" 5/16"-24 24 6.9 17/64" 3/8"-24 24 8.5 21/64" 7/16"-20 20 9.9 25/64" 1/2"-20 20 11.5 29/64" 9/16"-18 18 13.1 33/64" 5/8"-18 18 14.7 37/64" 3/4"-16 16 17.5 11/16" 7/8"-14 14 20.6 13/16" 1"-12 12 23.4 59/64" 1-1/8"-12 12 26.6 1-3/64" 1-1/4"-12 12 29.8 1-3/16" 1-3/8"-12 12 33.0 1-5/16" 1-1/2"-12 12 36.5 1-7/16" Related AIMS Selectors & Guides This page sits at the centre of AIMS's threading and drilling tool cluster. The related selectors and selection guides below go deeper on the choices around it: Tap & Die Selection Guide — what tap type for which material, hole type, and machine Drill Bit Selection Guide — HSS vs cobalt vs carbide, jobber vs stub vs reduced shank Cutting Speeds & Feeds Reference — Vc and feed rate by material and tool type Cutting Tool Materials — HSS, cobalt, carbide, PCBN, PCD compared Cutting Tool Coatings — TiN, TiAlN, AlCrN, when each matters Cutting Tool Troubleshooting — broken taps, walking drills, poor finish, oversize holes Metric / Imperial / Gauge Conversion Master Chart — full drill bit + thread size cross-reference Thread Standards: BSP vs NPT vs UNC — identify the thread system you're dealing with Or browse the full taps range + jobber drill bits + cobalt drill bits — Sutton primary stock, Bordo and P&N alternates, specialty brands available for next-day Australia-wide dispatch from our Milperra warehouse.Frequently Asked Questions What drill size for M3 tap? For M3 coarse thread (0.5mm pitch), use a 2.5mm tap drill. For M3 fine (0.35mm pitch), use a 2.65mm drill. Formula: 3 − 0.5 = 2.5mm. What drill size for M4 tap? For M4 coarse thread (0.7mm pitch), use a 3.3mm tap drill. For M4 fine (0.5mm pitch), use a 3.5mm drill. Formula: 4 − 0.7 = 3.3mm. What drill size for M5 tap? For M5 coarse thread (0.8mm pitch), use a 4.2mm tap drill. For M5 fine (0.5mm pitch), use a 4.5mm drill. Formula: 5 − 0.8 = 4.2mm. What drill size for M6 tap? For M6 coarse thread (1.0mm pitch), use a 5.0mm tap drill. For M6 fine (0.75mm pitch), use a 5.25mm drill. Formula: 6 − 1.0 = 5.0mm. What drill size for M8 tap? For M8 coarse thread (1.25mm pitch), use a 6.8mm tap drill. For M8 fine (1.0mm pitch), use a 7.0mm drill. Formula: 8 − 1.25 = 6.75mm, rounded to 6.8mm. What drill size for M10 tap? For M10 coarse thread (1.5mm pitch), use an 8.5mm tap drill. For M10 fine (1.25mm pitch), use 8.75mm; for M10 fine (1.0mm pitch), use 9.0mm. Formula: 10 − 1.5 = 8.5mm. What drill size for M12 tap? For M12 coarse thread (1.75mm pitch), use a 10.2mm tap drill. For M12 fine (1.5mm pitch), use 10.5mm; for M12 fine (1.25mm pitch), use 10.75mm. Formula: 12 − 1.75 = 10.25mm, rounded to 10.2mm. What drill size for M14 tap? For M14 coarse thread (2.0mm pitch), use a 12.0mm tap drill. For M14 fine (1.5mm pitch), use 12.5mm. Formula: 14 − 2.0 = 12.0mm. What drill size for M16 tap? For M16 coarse thread (2.0mm pitch), use a 14.0mm tap drill. For M16 fine (1.5mm pitch), use 14.5mm. Formula: 16 − 2.0 = 14.0mm. What drill size for M20 tap? For M20 coarse thread (2.5mm pitch), use a 17.5mm tap drill. For M20 fine (2.0mm pitch), use 18.0mm; for M20 fine (1.5mm pitch), use 18.5mm. Formula: 20 − 2.5 = 17.5mm. What drill size for 1/4 inch BSP tap? The recommended tap drill for 1/4 inch BSP (19 TPI) is 11.8mm, or 0.465 inches. This applies to both BSPP (parallel) and BSPT (taper) threads — the tap drill is the same. What drill size for 1/8 inch NPT tap? The recommended tap drill for 1/8 inch NPT (27 TPI) is 8.6mm, or 21/64 inch. NPT is a tapered thread used on American pipe fittings — distinct from BSP. What drill size for 1/4 inch UNC tap? For 1/4-20 UNC, use a 5.1mm tap drill (13/64 inch). UNC has 20 threads per inch and is the standard US coarse thread. How do I calculate tap drill size for metric threads? Tap drill size (mm) equals thread diameter minus thread pitch. Example: M10 × 1.5 = 10 − 1.5 = 8.5mm. This gives approximately 75% thread engagement, which is standard for most applications. What is a tap drill size? A tap drill size is the diameter of the hole you drill before cutting a thread with a tap. It must be smaller than the thread's outer diameter so the tap has material to cut the thread profile into. What is the difference between BSPP and BSPT? BSPP (British Standard Pipe Parallel) has straight threads and seals with an O-ring or washer. BSPT (British Standard Pipe Taper) has a tapered thread that seals as it tightens. Both share the same tap drill size for a given nominal size, but BSPT taps are designed to cut a taper. If a tap breaks during the threading process, see our guide on how to remove a broken tap — covering all six removal methods from tap extractors through to EDM. Ready to tap? Shop our full range of taps, dies & threading tools From metric hand taps to imperial die sets — AIMS Industrial stocks threading tools for every standard, ready to ship Australia-wide. Browse taps Talk to a specialist For the tap type that matches your hole and material, see our Tap Types Explained guide. For choosing the right cutting fluid for your material, see our Tap Magic cutting fluid guide. Need to identify a thread standard? Our Thread Standards Guide covers BSP, NPT, UNC, UNF, BSW and metric with identification tips. People Also Ask — Tap Drill Size Chart: Metric & Imperial Thread Sizes Q: What drill size do I use for an M10 tap? For M10 × 1.5 coarse thread, use an 8.5 mm pilot drill. For M10 × 1.25 fine thread, use a 8.75 mm drill (often rounded to 9.0 mm in practice). Using the correct pilot hole is critical — too small risks tap breakage; too large produces insufficient thread engagement and weak joints. Q: What is the difference between a taper tap and a plug tap? A taper tap has a long chamfer (8–10 threads) that guides it into the hole gradually — best for starting threads in blind or through holes. A plug tap (4–5 thread chamfer) picks up where the taper left off and is the most common general-purpose tap. A bottoming tap has just 1–2 threads of chamfer for cutting threads to the very bottom of a blind hole. Q: What is the difference between BSP and NPT threads? BSP (British Standard Pipe) uses a 55° thread angle and is the standard for most Australian, British, and European hydraulic and pneumatic fittings. NPT (National Pipe Taper) uses a 60° thread angle and is common on American equipment. The two are not interchangeable — mismatching causes leaks and can damage fittings even if they appear to thread together. Q: How do I know which tap size to buy? Match the tap to the bolt thread you need — an M6 × 1.0 tap cuts the thread for an M6 coarse bolt. Always pair taps with the correct pilot drill from a tap drill chart. For blind holes, buy a taper, plug, and bottoming tap set. For through holes, a plug tap alone is usually sufficient for most trade applications. For machining, see our machining range stocked across Australia. Looking for long drill bits? Our long drill bits range covers the common sizes and brands.
Read more
Tap Types Explained: Taper, Plug, Bottoming, Spiral Point & Flute
Choosing the right tap looks simple until you've snapped one off in a $400 casting. Then you find out the hard way that taper, plug, bottoming, spiral point and spiral flute taps aren't interchangeable — each does a specific job, and using the wrong one in the wrong hole is the fastest route to a broken tool. This guide walks you through every tap type Australian tradies and machinists actually use, with the forum-tested rules for matching the tap to the job. Tap Types — Quick Reference Tap Type Best For Chip Direction Hole Type Taper tap Starting threads by hand Sideways (straight flute) Through or blind (start only) Plug tap General-purpose threading Sideways (straight flute) Through holes Bottoming tap Full threads to base of blind hole Sideways (straight flute) Blind holes (after starter tap) Spiral point (gun) Production tapping in a machine Forward (ahead of tap) Through holes only Spiral flute Blind holes in tough materials Backward (out of hole) Blind holes only Forming (roll) tap Strongest threads, ductile materials No chips (cold-forms) Through or blind The single most common forum mistake: putting a spiral point (gun) tap in a blind hole. The chips have nowhere to go — they pack up at the bottom and snap the tap. Gun taps need somewhere for chips to exit ahead of the cutting flutes. For blind holes, use a spiral flute tap instead. For tap drill sizes, see our Tap Drill Size Chart. For thread standards (BSP, NPT, UNC, UNF, metric), see our Thread Standards Guide. What Is a Tap? A tap is a hardened cutting tool used to create internal threads in a pre-drilled hole. The tap is essentially a precision-ground threaded rod with cutting edges along its length. As you rotate it into a hole sized correctly for the tap, the cutting edges remove material to form the thread profile. Three things define every tap: Thread profile — metric M-series, UNC, UNF, BSW, BSP — must match the thread standard you want to cut. See our Thread Standards Guide for the differences. Chamfer length — the tapered cutting section at the start of the tap. Long chamfer (4–8 threads) for starting, short chamfer (1–2 threads) for cutting threads to the bottom of a blind hole. Flute design — straight, spiral point, or spiral flute. This determines where the chips go as you cut. Match all three to the job and you'll cut clean threads first time. Get one wrong and you'll likely break the tap, strip the thread, or get a hole you can't use. The Three Classical Hand Taps — Taper, Plug, Bottoming Most threading is still done with the traditional set of three straight-flute hand taps. The only difference between them is the length of the chamfered cutting section at the tip — the threads themselves are identical. Taper Tap (4–8 chamfered threads) The taper tap has the longest cutting chamfer — typically 7 to 10 threads of taper at the tip, gradually working up to full thread depth. The long taper does two things: Makes it easy to start the thread square to the hole by hand Distributes the cutting load across many threads, reducing torque and breakage risk Taper taps are the safest tap to start a thread with, especially for tradies tapping by hand without a guide. The trade-off is that you can't cut full threads to the bottom of a blind hole — the tapered tip means the last 7 threads at the bottom are progressively shallower. Plug Tap (3–5 chamfered threads) The plug tap (sometimes called the "second tap") has a shorter chamfer than the taper — usually 3 to 5 threads. It's the workhorse of hand tapping: For through holes, you can start and finish with just a plug tap For blind holes, use it as the second pass after the taper tap to deepen the threads For machine tapping straight-flute work, plug is typically the default If you're only going to buy one hand tap of a given size, make it a plug. Bottoming Tap (1–2 chamfered threads) The bottoming tap has almost no chamfer — usually just 1 to 2 threads of cutting taper at the tip. This lets it cut full threads right down to the bottom of a blind hole. Critical detail tradies often get wrong: a bottoming tap cannot start a thread on its own. With only 1–2 threads of chamfer, it doesn't have the lead-in to stay square in a hole. You must always start with a taper or plug tap first, then finish with the bottoming tap. If you put a bottoming tap into a fresh hole and try to cut threads with it from scratch, it will skate sideways, chip, or break. When to Use Each — Decision Logic Situation Sequence Through hole, easy material Plug tap only Through hole, tough material Taper → plug Blind hole, threads not needed at base Taper → plug Blind hole, full threads to base required Taper → plug → bottoming Hand tapping a sensitive material first time Always start with taper Hand tap sets sold in Australia typically come as a three-piece set (taper, plug, bottoming) in each thread size — see our Imperial Hand Taps and Tap and Die Sets collections. Spiral Point vs Spiral Flute — The #1 Confusion This is the question that breaks more taps than any other: spiral point and spiral flute taps look almost identical, and tradies who haven't worked with both can't tell them apart in a tool drawer. They are designed for opposite jobs. Get them mixed up and you'll snap a tap inside a workpiece. Spiral Point Tap (also called Gun Tap, Bull Nose Tap) A spiral point tap has straight flutes along its length, but the cutting chamfer at the tip is ground with a slight angled "point" geometry that pushes chips forward, ahead of the cutting edge. The chips clear out through the bottom of the hole. This makes spiral point taps brilliant for: Through holes — chips exit the bottom of the hole, never building up around the tap Production machine tapping — high speed, continuous rotation, no need to back off Soft and stringy materials like aluminium, brass and copper where chips tend to weld to a cutting tap Spiral point taps are also called "gun taps" because the chip-shooting action looks like a rifle barrel ejecting cartridges. Critical warning: NEVER use a spiral point tap in a blind hole. The chips have nowhere to go. They pack up at the bottom of the hole, the tap binds, and it snaps. This is the most common forum-reported broken-tap scenario. See our Metric Spiral Point Taps and Imperial Spiral Point Taps ranges. Spiral Flute Tap A spiral flute tap has helical flutes running along its length, similar to a drill bit. The helix direction pulls chips backward, out of the hole as the tap rotates. This makes spiral flute taps the right choice for: Blind holes — the upward chip flow keeps the bottom of the hole clear Tough materials like stainless steel, alloy steel, and titanium where good chip evacuation prevents work-hardening Deep threading where chips have a long way to travel before exiting Use a spiral flute tap in a through hole and you'll get a worse result than a plug — the helical chip flow pulls chips back through the cutting threads, sometimes re-cutting them. Spiral flute should mostly stay in blind-hole work. See our Metric Spiral Flute Taps and Imperial Spiral Flute Taps. How to Tell Spiral Point and Spiral Flute Apart Feature Spiral Point (Gun) Spiral Flute Flutes along body Straight (parallel to axis) Helical (twisted like a drill) Chamfer geometry Angled "point" at tip Standard cutting chamfer Chip direction Forward (out bottom) Backward (out top) Use in through holes ✓ Excellent ✗ Avoid Use in blind holes ✗ Will snap ✓ Excellent The visual giveaway is the flute geometry — if the flutes are straight (parallel to the tap axis), it's spiral point. If the flutes spiral around the tap like a drill bit, it's spiral flute. The chamfer geometry difference is harder to see without comparing two side by side. Hand Taps vs Machine Taps Hand taps and machine taps look similar but are engineered for different working conditions. Hand Taps Hand taps are designed for manual use with a tap wrench. They typically come as a three-piece set (taper, plug, bottoming) and have straight flutes for general-purpose threading. The expectation is that the user will rotate the tap forward 1/2 to 1 turn, then back off 1/4 to 1/2 turn to break the chip — this is essential for chip clearance with straight-flute geometry. Hand taps work fine in machine spindles too, especially for small-batch work. But for production tapping, machine taps cut faster and cleaner. Machine Taps Machine taps (also called CNC taps) are designed for continuous high-speed rotation in a tapping head, drill press, lathe, or CNC machine. They're typically: Spiral point or spiral flute (so they don't need backing off to break chips) Made from tougher materials (HSS-E cobalt, HSS-PM, or carbide) Often coated for higher cutting speeds Ground to tighter tolerances for repeatable thread quality If you're tapping the same thread hundreds of times a day, a machine tap pays for itself in cycle time and tool life. For one-off jobs or maintenance work, a hand tap set is more economical. Forming Taps (Roll Taps) — Cold-Forming Threads Forming taps (also called roll taps, fluteless taps or thread-rolling taps) are a fundamentally different way to make a thread. Instead of cutting and removing material, a forming tap displaces the workpiece material — it cold-forms the thread profile by pressing the metal into the thread shape. Forming taps have no flutes (no chip path is needed because there are no chips), no cutting edges, and a smooth polygonal cross-section that does the forming work. Advantages of forming taps: Stronger threads — the cold-worked metal grain follows the thread profile rather than being cut across it, increasing thread strength by 10–40% No chips — eliminates chip evacuation problems and chip welding in soft materials Longer tool life — no cutting edges to dull or break Higher feed rates — typically 30–50% faster than cutting taps Smaller tap drill — forming taps use a slightly larger pilot hole than cutting taps Strict limits — forming taps DON'T work on: Cast iron (brittle — will crack instead of forming) Hardened steel above ~30 HRC Most plastics (cold flow won't hold thread shape) Materials with less than ~5% elongation Forming taps are best suited to aluminium alloys, low-to-medium carbon steel, copper, brass (soft), and other ductile metals. See Metric Thread Forming Taps for our range. Tap Materials — HSS, HSS-E, HSS-PM, Solid Carbide The material the tap itself is made from determines its hardness, toughness, heat resistance, and price. Match the tap material to the workpiece material and the production rate. HSS (High-Speed Steel) HSS is the workhorse tap material. Tough, takes a sharp edge, holds up well to general-purpose threading in mild steel, aluminium, brass, plastics, and most workshop materials. M2 HSS is the most common grade. Affordable enough that breaking one isn't a disaster. Limitation: HSS softens at sustained cutting temperatures above ~600°C. Not the right pick for high-speed production work or work-hardening stainless steel. HSS-E (HSS-Co, Cobalt HSS) HSS-E adds 5–8% cobalt to HSS, increasing hot hardness — the ability to retain cutting hardness at high temperatures. This makes HSS-E better suited to: Stainless steel (which work-hardens and generates heat) Heat-resistant alloys Higher cutting speeds where HSS would soften Production tapping where consistent edge life matters HSS-E is typically 20–40% more expensive than plain HSS but lasts considerably longer in tough materials. HSS-PM (Powder Metallurgy HSS) HSS-PM is made by powder metallurgy rather than melted-and-rolled steel. The fine grain structure gives it better toughness than HSS-E with similar or higher hardness. Use cases: Very hard alloys Tool steel and die work High-precision tapping where edge consistency matters Bridge between cobalt HSS and solid carbide Premium price, but still tougher than carbide — won't shatter if you stall it. Solid Carbide Solid carbide taps are extremely hard and wear-resistant, designed for high-volume CNC tapping in difficult materials. They allow much higher cutting speeds than any HSS variant. The trade-off is brittleness — carbide will shatter if you stall it, side-load it, or hit a hard inclusion. Carbide taps need a rigid setup, precision-controlled feed, and a tap holder with sufficient tension/compression compensation. Not for hand tapping. Tap Coatings — Black Oxide, TiN, TiCN, TiAlN Surface coatings reduce friction, improve chip flow, and extend tap life. Common coatings you'll see on Australian shelves: Black oxide / steam tempered — a thin oxide layer that reduces galling in mild steel and improves lubricant retention. Cheap and reliable for general-purpose work. TiN (Titanium Nitride) — gold-coloured coating, ~2,300 HV hardness, good general-purpose coating that extends tap life in steel and stainless. TiCN (Titanium Carbonitride) — blue-grey or grey-purple, harder than TiN (~3,000 HV), good for cast iron and harder steels. TiAlN (Titanium Aluminium Nitride) — violet-grey or dark grey, very hard (~3,300 HV), excellent heat resistance — the premium choice for stainless, high-temp alloys, and hardened materials at high cutting speeds. For most workshop tapping, an uncoated or black-oxide HSS tap with proper cutting fluid is fine. Move up to TiN or TiAlN when you're tapping stainless, working at production rates, or running unattended CNC tapping cycles. How to Choose a Tap by Workpiece Material Material is the single biggest factor in tap selection. Get the material match right and you'll cut clean threads with a tap that lasts. Aluminium and Aluminium Alloys Aluminium tapping has one big problem: the chips weld to a hot HSS cutting tap and clog the flutes — known as "BUE" (built-up edge) on machinist forums. The result is a torn-looking thread with chunks of aluminium stuck to it. Fixes that work: Use a spiral point (gun) tap at higher cutting speed — gets chips out before they weld Use a forming tap — no chips at all, beautiful threads, ideal for aluminium Lubricate generously with kerosene, methylated spirits, or a dedicated aluminium-tapping fluid (see our Tap Magic cutting fluid guide for variant selection) — water-soluble coolants alone aren't enough Don't dwell — keep the tap moving so chips don't weld Mild Steel The easiest material to tap. HSS plug tap or spiral point (through holes), spiral flute (blind holes). General-purpose cutting fluid. Hand tapping or machine tapping both work well. This is what most workshop tapping looks like. Stainless Steel Stainless is the material that breaks more taps than any other — and forums are full of advice about it because most of that advice is wrong. The key facts: Stainless work-hardens. If the tap "rides" the surface without cutting (because it's dull, you're going too slow, or there's no cutting fluid), the surface hardens and the next tap breaks trying to cut into it. Use HSS-E (cobalt) or HSS-PM taps, not plain HSS. The hot hardness matters here. Use sulfurised cutting oil ("dark cutting oil") — water-based coolants alone aren't enough. The sulfur prevents chip welding. Spiral flute for blind holes, spiral point for through. Don't compromise here. Cutting speed: slower than you think. Roughly 1/3 to 1/2 the speed you'd use for mild steel. Engage the cutting edge immediately. Never let the tap idle on the surface. Cast Iron Cast iron tapping is the opposite of stainless — it cuts easily but throws abrasive dust instead of chips. Use: Straight-flute or spiral point HSS or HSS-E taps NO cutting fluid (cast iron is self-lubricating; fluid just turns dust to paste) Compressed air to clear chip dust Never use forming taps on cast iron — it's brittle and will crack instead of forming Brass and Bronze Brass is forgiving — almost anything works. Standard HSS plug tap, light cutting oil, moderate speed. Bronze is similar but harder, so prefer HSS-E for production work. Watch out for "gummy" brass alloys that grab the tap — back off frequently to break chips. Plastic For most plastics (acrylic, nylon, polycarbonate, ABS), use a sharp HSS tap with shallow chamfer, slow speed, and dry cutting. No forming taps (plastic creeps and won't hold a formed thread). For abrasive filled plastics (glass-filled nylon, carbon-filled), use a TiN-coated tap for better wear life. Why Taps Break — and How to Avoid It "Why do my taps keep breaking?" is the #1 forum question in tapping. The answer is almost always one of these: Wrong tap for the hole type. Spiral point in a blind hole = packed chips = broken tap. Bottoming tap as a starter = skating tap = broken tap. Wrong tap drill size. Too small a hole means the tap has to cut too much material per thread. Always verify against a Tap Drill Size Chart before drilling. No cutting fluid. Friction heat softens the tap, chips weld, breakage follows. Even on "easy" materials. Not backing off for chip break. Straight-flute hand taps need a 1/4 to 1/2 reverse turn for every 1 to 2 forward turns to break chips. Forget this and the chips pack up. Wrong material match. Plain HSS in stainless = work-hardened surface = broken tap on the next try. Use HSS-E or HSS-PM. Tap not square to the hole. Side-loading a tap as it cuts puts a bending stress that taps don't handle well. Use a tapping guide or set up in a machine. Forcing through resistance. If a tap suddenly gets harder to turn, STOP. Back it out, clear chips, check for binding, and continue. Don't crank harder. Riding the surface without cutting (stainless especially) — work-hardens the material and breaks the next tap. If you do break a tap, see our Screw Extractors for tap removal tools. Alternatives: EDM tap disintegration (specialist service), or carbide-burr the broken tap out (last resort, damages the thread). Tap Speed and Cutting Fluid Cutting speed for tapping is dramatically slower than for drilling. Approximate starting speeds for HSS hand taps: Material SFM Approx RPM for M10 Aluminium 50–100 500–1000 Brass / bronze 50–100 500–1000 Mild steel 30–60 300–600 Cast iron 20–40 200–400 Stainless steel 10–20 100–200 Tool steel (annealed) 10–20 100–200 HSS-E and HSS-PM taps can run 50–100% faster than these numbers. Solid carbide can run faster still, but only in rigid machine setups. Cutting fluid pairings: Mild steel, cast steel: standard tapping fluid or sulfurised cutting oil Stainless steel, alloy steel: sulfurised cutting oil ("dark oil") Aluminium: kerosene, methylated spirits, or dedicated aluminium-cutting fluid Brass, bronze: light mineral oil or dry Cast iron: dry (compressed air for chip removal) Plastic: dry, or water-based mist for filled plastics See Cutting Lubricants for our range. Sutton Tools — Australian-Made Cutting Tools Sutton Tools is Australia's largest manufacturer of HSS cutting tools, based in Thomastown, Victoria, and Australian-owned and operated since 1917. Their tap range is genuinely made in Australia (not just badged) — Sutton manufactures everything from the steel grinding through to coating in their Thomastown plant. The Sutton tap range covers: Premium HSS Blue series — bright, cobalt-tough, suited to mild steel, alloy steel and stainless Premium HSS Ni — for nickel alloys and tough stainless grades Tinite coated — TiN-coated for extended life R45 series — proprietary geometries for difficult materials (W, Al, VADH variants for steel, aluminium and high-strength materials) Spiral flute, spiral point and straight flute in metric (M3 to M30) and imperial (UNC, UNF, BSW, BSP) Sutton taps carry the Australian Made & Owned certification. For Australian Industry Capability (AIC), Buy Australian, mining local content and government procurement requirements, Sutton ticks every box. See our Sutton Tools collection or browse all our Taps. AIMS Tap Product Cross-Reference Sourcing taps and threading tools from AIMS Industrial by category: Hand taps (metric & imperial): Imperial Hand Taps Spiral point (gun) taps — metric: Metric Spiral Point Taps Spiral point (gun) taps — imperial: Imperial Spiral Point Taps Spiral flute taps — metric: Metric Spiral Flute Taps Spiral flute taps — imperial: Imperial Spiral Flute Taps Straight flute taps — metric: Metric Straight Flute Taps Straight flute taps — imperial: Imperial Straight Flute Taps Thread forming (roll) taps: Metric Thread Forming Taps Machine nut taps: Metric Machine Nut Taps | Imperial Machine Nut Taps Complete tap and die sets: Tap and Die Sets Thread identification gauges: Screw Pitch Gauges Tap extractors (broken tap removal): Screw Extractors Cutting fluids: Cutting Lubricants Full threading range: Threading Collection Related Reference Articles Tap Drill Size Chart — Metric & Imperial (drill size for every tap) Thread Standards Guide — BSP vs NPT vs UNC Tap Drill Diameters Explained — Major, Minor & Pitch Drill Bit Size Chart — Metric, Imperial, Fractional Repairing stripped threads rather than starting fresh? Our Stripped Threads Repair Guide walks the escalation ladder — re-tap, oversize, Helicoil, TimeSert and weld-up. Frequently Asked Questions What is the difference between a taper, plug and bottoming tap? The difference is the length of the chamfered cutting section at the tip. Taper taps have 7–10 chamfered threads (longest, easiest to start). Plug taps have 3–5 chamfered threads (most common general-purpose tap). Bottoming taps have only 1–2 chamfered threads, allowing them to cut full threads to the bottom of a blind hole — but they can't start a thread on their own; you must use a taper or plug first. What is the difference between a spiral point and a spiral flute tap? A spiral point (gun) tap pushes chips forward, ahead of the tap — use it in THROUGH holes only. A spiral flute tap pulls chips backward, up out of the hole — use it in BLIND holes only. The flute geometry on the tap body is the visual giveaway: straight along the axis = spiral point; helical like a drill bit = spiral flute. Using one in the wrong hole type is the #1 cause of broken taps. What is a gun tap? "Gun tap" is the common workshop name for a spiral point tap. The name comes from the way it ejects chips forward, ahead of the cutting edge, like a gun ejecting cartridges. Gun taps are ideal for through-hole production machine tapping. Never use them in blind holes — the chips will pack and snap the tap. Can a bottoming tap start a thread? No. A bottoming tap has only 1–2 threads of chamfer, which isn't enough lead-in to keep the tap square in a fresh hole. It will skate sideways, chip, or break. Always start the thread with a taper or plug tap first, then use the bottoming tap to finish the thread to the base of a blind hole. What tap should I use for aluminium? A spiral point (gun) tap for through holes, or a forming (roll) tap for either through or blind. Aluminium chips weld to a standard cutting tap as it heats up — gun taps clear chips fast enough to avoid this, and forming taps produce no chips at all. Use kerosene, methylated spirits, or a dedicated aluminium tapping fluid as lubricant. Never tap aluminium dry. What tap should I use for stainless steel? An HSS-E (cobalt HSS) or HSS-PM tap, ideally with TiAlN coating. Spiral flute for blind holes, spiral point for through. Use sulfurised cutting oil (dark cutting oil) — not water-based coolant alone. Cut at 1/3 to 1/2 the speed you'd use for mild steel, and never let the tap "ride" on the surface without cutting, or the stainless will work-harden and break your next tap. Why do my taps keep breaking? The most common causes are: spiral point tap in a blind hole (chips pack), wrong tap drill size (hole too small), no cutting fluid, not backing off chips with straight-flute hand taps, wrong material match (plain HSS in stainless), tap not square to the hole, or forcing through resistance. Stop the moment a tap suddenly gets harder to turn — clear chips, check alignment, and continue. Hand tap or machine tap — which do I need? For one-off jobs, maintenance work, and small production runs, hand taps (taper, plug, bottoming three-piece sets) used with a tap wrench or in a drill press are fine. For production tapping at high volume, machine taps (typically spiral point or spiral flute, HSS-E or coated) cut faster and don't require backing off. Hand taps work in machines too, just slower. What is a forming tap (roll tap)? A forming tap cold-forms the thread by displacing material — no cutting, no chips. The resulting thread is 10–40% stronger than a cut thread because the metal grain follows the thread profile. Forming taps work on ductile materials (aluminium, low-carbon steel, copper) but cannot be used on cast iron, hardened steel, brittle materials, or most plastics. They require a slightly larger pilot hole than cutting taps. What does HSS-E mean? HSS-E is high-speed steel alloyed with 5–8% cobalt (also called HSS-Co or "cobalt HSS"). The cobalt addition increases hot hardness — the tool's ability to retain hardness at elevated cutting temperatures. HSS-E taps last considerably longer than plain HSS in stainless steel, alloy steel and at higher cutting speeds. What is HSS-PM tap material? HSS-PM (Powder Metallurgy HSS) is high-speed steel made by powder metallurgy rather than melted-and-rolled steel. The fine, even grain structure gives it better toughness than cobalt HSS with similar or higher hardness. It sits between HSS-E and solid carbide in price and performance — used for tough materials, tool steel, and precision tapping where consistent edge life matters. What is the difference between a tap and a die? A tap cuts internal threads (in a hole). A die cuts external threads (on a rod or pipe). Tap-and-die sets pair both tools at matching thread sizes so you can create or repair both sides of a threaded joint. See our Tap and Die Sets for combined kits. Do I need cutting fluid when tapping? Yes — for almost every material except cast iron. Even on mild steel where the tap feels easy, cutting fluid extends tap life dramatically, improves thread surface finish, reduces breakage risk, and prevents chip welding. Cast iron is the exception — its graphite content makes it self-lubricating, and adding fluid turns the chip dust to abrasive paste. How fast should I tap? Tapping speed is much slower than drilling. As a starting point with HSS taps: aluminium and brass 50–100 SFM, mild steel 30–60 SFM, cast iron 20–40 SFM, stainless steel 10–20 SFM. HSS-E (cobalt) taps can run 50–100% faster. If a tap chatters, screams, or smokes, slow down and add cutting fluid. What does the "chamfer" of a tap mean? The chamfer is the tapered cutting section at the tip of the tap, where the cutting edges aren't yet at full thread depth. The chamfer length is what distinguishes taper taps (7–10 chamfered threads), plug taps (3–5), and bottoming taps (1–2). A longer chamfer is easier to start but can't cut threads near the bottom of a blind hole. People Also Ask — Tap Types Q: What are the three classical hand tap types and how do they differ? The three classical hand taps are taper, plug, and bottoming. A taper tap has the most chamfered lead threads, making it easiest to start but unable to cut to the bottom of a blind hole. A plug tap has fewer lead threads and is the most common general-purpose choice. A bottoming tap has just one or two lead threads and cuts threads to the very base of a blind hole. Q: What is the difference between a spiral point tap and a spiral flute tap? A spiral point (gun) tap pushes chips forward ahead of the cut and is used in through holes where chips can exit from the far end. A spiral flute tap pulls chips back up and out, suited to blind holes where chips cannot be pushed through. Using the wrong type in a blind hole is one of the most common causes of tap breakage. Q: What is a forming (roll) tap and when would you use it? A forming or roll tap displaces material to create threads rather than cutting them, producing no chips. This gives stronger threads and is well suited to ductile materials such as aluminium and low-carbon steel. Forming taps cannot be used in brittle materials, which will crack rather than form. Q: When should you use a machine tap rather than a hand tap? Machine taps are designed to run in a power tapping head, CNC machine, or cordless drill at controlled speed and feed. Hand taps are designed for manual use where the operator can feel resistance and reverse to break chips. Using a hand tap in a power machine without controlled feed typically results in tap breakage. Q: Why is starting with a taper tap important for hand tapping? The chamfered lead on a taper tap helps align the tap square to the hole before the cutting threads engage. Starting square is critical — a tap driven at an angle cuts a crooked thread and is prone to breakage, particularly in blind holes and harder materials. AIMS Industrial stocks machining — see the full range for trade and industrial use.
Read more