Tap selection comes down to three questions: blind hole or through hole, what material are you threading, and is it a hand-driven or machine-driven operation? Through holes in steel typically take a spiral point tap (pushes chips forward, out of the hole). Blind holes take a spiral flute tap (pulls chips back up out of the hole). Hand-tapping with a tap wrench uses hand taps — usually in taper, plug and bottoming progression. Ductile materials like aluminium and copper alloys can be threaded with thread forming taps that produce stronger, chipless threads. For external threads on round stock, use dies (split, button or die-nut style).
This guide walks through every tap and die type AIMS stocks, when to use each, how to select for thread system (metric, BSP, BSPT, NPT, UNC, UNF, BSW, BSF), what drill size to use before tapping, and which brand wins where. AIMS holds one of Australia's deepest tap and die ranges — 599 tap product lines and 179 die product lines across Sutton Tools (engineering dominant), Bordo (workshop and specialty), plus tap-and-die-sets, tap wrenches and die holders. We'll recommend honestly across them.
Quick Reference: Which Tap for Which Hole?
The fastest selection table. Match the hole condition + workpiece material to the right tap geometry. For complete tap drill sizes, see the Threading & Tap Drill Size Chart.
| Hole Type | Workpiece Material | Recommended Tap Type | Why | AIMS Range |
|---|---|---|---|---|
| Through hole | Mild steel | Spiral point (gun) tap, HSS | Pushes chips forward out the bottom of the hole | Metric Spiral Point Taps |
| Through hole | Stainless 304/316 | Spiral point, HSS-Co or PM-HSS, TiCN-coated | Cobalt content + lubricious coating for work-hardening alloys | Sutton spiral point cobalt range |
| Blind hole | Mild steel | Spiral flute tap, HSS | Helical flutes pull chips backwards out of the hole | Metric Spiral Flute Taps |
| Blind hole | Stainless 304/316 | Spiral flute, HSS-Co or PM-HSS, TiCN-coated | Cobalt for hot hardness + chip evacuation | Sutton spiral flute cobalt range |
| Through or blind | Aluminium & ductile alloys | Thread forming (fluteless) tap | Cold-forms thread — no chips, 30-40% stronger thread | Metric Thread Forming Taps |
| Hand-tapped (with tap wrench) | All | Hand tap set (taper, plug, bottoming) | Three-step progression eases manual cutting effort | Metric Hand Taps / Imperial Hand Taps |
| Production nut tapping | Mild steel nuts | Machine nut tap (long shank) | Designed for high-volume nut tapping — tap stays with the work | Machine Nut Taps |
| Cast iron | Grey or ductile | Straight flute HSS, plug or bottoming | CI produces fine chips that don't need spiral evacuation | Sutton straight-flute range |
| Brass / copper | Free-machining | Straight flute HSS, plug | Brass chips break short — chip evacuation simple | Sutton or Bordo HSS hand taps |
| Hardened steel (over 35 HRC) | Tool steel, dies | Solid carbide tap or special HSS-PM | Standard HSS won't survive — needs carbide or premium PM-HSS | Special order — contact AIMS |
For tap drill sizes (e.g. M8 x 1.25 = 6.8mm drill), the tap drill size chart covers metric coarse + fine, UNC, UNF, BSW, BSF, BSP and NPT.
Tap Types — The Six Major Categories
Every tap AIMS stocks falls into one of six functional categories. Choosing the right one is far more important than the brand or coating — wrong tap type for the job means tap breakage or thread quality below standard.
1. Hand Taps (Taper, Plug, Bottoming)
Hand taps are designed for tap-wrench use rather than machine driving. They come as a three-tap progression in the same thread size:
- Taper tap — 7-10 leading threads ground tapered. Easiest to start by hand. Use first for a new thread.
- Plug tap (intermediate) — 3-5 leading tapered threads. Common single-tap choice for through holes where the full thread is reached at the bottom.
- Bottoming tap — 1-2 leading tapered threads. Use last in a blind hole to thread close to the bottom. Cannot start a thread — only finishes one.
The taper-plug-bottoming progression is the original hand-tapping system. Many workshops use a plug tap as the single-tap default and only step to the taper or bottoming when the application calls for it.
Buy hand taps for: manual tapping with a tap wrench, blind holes where you need to thread close to the bottom (use bottoming), one-off thread cutting, sensitive feel work where you want to feel the resistance.
AIMS stocks 43 metric hand tap lines and 63 imperial hand tap lines from Sutton Tools and Bordo.
2. Spiral Point Taps (Gun Taps) — For Through Holes
Spiral point taps have a slight helical (15-25 degree) groove ground into the cutting face just behind the tip. As the tap turns, this groove pushes chips forward and out the bottom of the hole. The flutes themselves are straight or near-straight.
Critical rule: spiral point taps require an OPEN hole bottom — chips must have somewhere to go. They are designed for through holes only.
What you get: faster cutting, no chip jamming in the flute, cleaner threads, longer tool life. Spiral point is the production standard for through holes in steel, stainless and aluminium.
Buy spiral point taps for: through holes in steel and stainless, production tapping, CNC tapping with rigid tap or floating tap holder, any application where you want chips to clear automatically.
Don't buy spiral point taps for: blind holes (chips will jam at the bottom), cast iron (chips don't form properly).
AIMS stocks 70 metric spiral point tap lines and 37 imperial spiral point tap lines.
3. Spiral Flute Taps — For Blind Holes
Spiral flute taps have helically-twisted flutes along the full length of the cutting portion — like a drill bit's spiral. The helix angle (15-35 degrees typically) pulls chips backwards out of the hole, away from the cutting edge.
This makes spiral flute taps the right choice for blind holes — chips evacuate up out of the hole rather than packing at the bottom. They also work in through holes but spiral point is usually faster there.
Spiral flute taps come in slow-helix (15°), medium-helix (25°) and fast-helix (35°) variants:
- Slow helix (15°): short-chip materials like cast iron, brass, aluminium
- Medium helix (25-30°): general-purpose for steel and stainless
- Fast helix (35-45°): long-chip ductile materials like aluminium, copper, soft steel
Buy spiral flute taps for: blind holes in any tappable material, deep threads, harder steels and stainless, CNC tapping.
AIMS stocks 80 metric spiral flute tap lines and 34 imperial spiral flute tap lines.
4. Thread Forming (Fluteless) Taps
Thread forming taps don't cut a thread — they cold-form it. The tap displaces material to produce the thread profile instead of cutting a chip. The result: no chips at all, stronger threads (30-40% stronger than cut threads because the grain flows around the thread instead of being severed), and zero chip jamming.
Critical limitation: thread forming only works in DUCTILE materials. Aluminium, copper alloys, brass (free-machining), low-carbon mild steel, austenitic stainless are all good. Cast iron, hardened steel, high-carbon steels and brittle materials cannot be thread-formed — they crack instead.
You also need a slightly larger drill size for thread forming than for cutting taps (since you're displacing material rather than removing it). Manufacturer charts give the correct drill diameter.
Buy thread forming taps for: aluminium production tapping (the dominant application), copper alloys, soft mild steel, austenitic stainless, any application where you need maximum thread strength or zero chips.
AIMS stocks 29 metric thread forming tap lines and 12 imperial thread forming tap lines from Sutton Tools.
5. Machine Nut Taps
Machine nut taps are designed for one specific job: high-volume nut production on automatic machines. The shank is extended and bent to accommodate the nut tapping head, and the tap stays in the work (loaded with nuts) rather than being threaded back out.
This is industrial production gear — not workshop tooling. Most readers won't need machine nut taps, but engineering production users will. AIMS stocks metric machine nut taps and imperial machine nut taps.
6. Straight Flute Taps
The original design — straight flutes parallel to the tap axis, no helix angle, no shaped point. Straight flute taps work in cast iron (where chips break short and clear naturally), free-machining brass, plastic and other materials where chip evacuation is automatic.
For modern steel tapping (especially CNC and production volumes), spiral point or spiral flute is usually faster. Straight flutes hold their place for cast iron, brass and plastics. Bordo offers a strong straight-flute range for the workshop tier; Sutton's straight-flute tier covers engineering work in cast iron and brass.
AIMS stocks 83 imperial straight flute tap lines.
Die Types — Cutting External Threads
Dies cut external threads on round stock. AIMS stocks 179 threading die lines across three main types:
Split (Adjustable) Dies
Round dies with a single radial slot cut through. A grub screw in the die holder squeezes the slot closed, letting you adjust the thread diameter. Loosen to take a lighter cut, tighten to take a heavier final pass. The split design is the workshop standard for one-off threading on round bar.
Buy split dies for: hand-threading round bar, where you need to adjust the cut depth, general workshop external thread cutting.
Solid (Button) Dies
Round dies without the slot. They cut to a fixed diameter only — no adjustment possible. Solid dies cut more accurately and last longer than split dies (no slot weakens the body), but they're a one-shot tool: if the diameter is wrong, you replace the die rather than adjust it.
Buy solid dies for: production threading where adjustment isn't needed, repeat work with known stock diameter, applications where thread accuracy matters more than flexibility.
Die Nuts (Rethread Dies)
Hexagonal-bodied dies designed to be driven with a standard spanner or socket. They have less cutting capability than full split or button dies — designed for cleaning up damaged threads on existing fasteners rather than cutting new threads from raw stock.
Common workshop use: cleaning rust or corrosion from bolt threads, restoring damaged threads after the bolt has been hit or distorted, refreshing threads after welding nearby.
AIMS stocks 70 die nut lines covering metric and imperial threads.
Die Holders & Stocks
The handle assembly that holds the die during cutting. Split dies need a die holder with both clamp screws and adjustment screw. Button dies use a simpler holder. Standard sizes: 1", 1-1/2", 2", 2-1/2" diameter to match common die sizes.
AIMS stocks die holders and stocks.
Thread Systems — Which Standard Do You Need?
The biggest cause of mismatched taps and dies isn't workmanship — it's buying the wrong thread system. Australia uses primarily metric for new construction, BSP/BSPT for fluid plumbing, BSW/BSF for legacy heritage work, NPT for some imported equipment and UNC/UNF for American imports. Match the thread system to the parent component:
| System | Full Name | Where Used | Identifier |
|---|---|---|---|
| Metric Coarse (M) | ISO Metric Coarse Thread (e.g. M8 x 1.25) | Default for Australian engineering, EU and most international | "M" prefix, e.g. M6, M8, M10, M12 |
| Metric Fine (MF) | ISO Metric Fine Thread (e.g. M8 x 1.0) | Aerospace, automotive, fine adjustments, harder materials | "M" prefix with explicit pitch, e.g. M8 x 1.0 |
| BSP / G | British Standard Pipe (parallel) | Fluid plumbing throughout Australia, hydraulics, pneumatics | "BSP" or "G" designation, e.g. G 1/2, BSP 3/4 |
| BSPT / Rc / R | British Standard Pipe Taper | Sealing pipe threads (gas, oil, hydraulic) | "BSPT", "Rc", "R" designation |
| NPT | National Pipe Taper (American) | US-sourced equipment, automotive imports, some hydraulics | "NPT" designation, e.g. 1/4 NPT |
| UNC | Unified National Coarse (American) | US-sourced fasteners and equipment | Fraction and TPI, e.g. 1/4-20 UNC |
| UNF | Unified National Fine (American) | US automotive, aerospace, precision work | Fraction and TPI, e.g. 1/4-28 UNF |
| BSW | British Standard Whitworth (coarse) | Heritage Australian and UK equipment, vintage machinery, restoration work | Fraction and TPI, 55° thread angle |
| BSF | British Standard Fine (Whitworth fine) | Heritage automotive, vintage UK equipment | Fraction and TPI, 55° thread angle |
Critical disambiguation: BSP and NPT are NOT interchangeable, even at the same nominal size. BSP uses a 55° thread angle, NPT uses 60°. Forcing them together damages both threads and creates a leaking joint. Always confirm the system before ordering.
For Whitworth threads (BSW/BSF) at the 55° angle, you also can't substitute UNC or metric taps. The angle mismatch produces immediate cross-threading. Identify the parent thread first.
For complete tap drill sizes (metric M3-M30, UNC 4-40 to 1-8, UNF 6-40 to 1-12, BSW 3/16-2", BSF 3/16-1-1/2", BSP 1/8 to 2", NPT 1/16 to 2"), see the comprehensive Threading & Tap Drill Size Chart.
Tap Drill Sizing — Get the Hole Right Before You Tap
The drill size before tapping is critical. Too tight and the tap snaps; too loose and the thread strips. Standard practice for cutting taps targets 75% thread engagement — an empirical sweet spot between thread strength and tapping torque.
Quick metric tap drill formula (cutting taps, 75% engagement): tap drill = major diameter − pitch. So for M8 x 1.25: 8.0 − 1.25 = 6.75mm (round to 6.8mm). For M10 x 1.5: 10.0 − 1.5 = 8.5mm. The formula gets you close enough for non-critical work; for precision tapping use the published tables.
Common metric coarse tap drill sizes:
| Thread | Pitch | Tap Drill (cutting tap) | Tap Drill (forming tap) |
|---|---|---|---|
| M3 x 0.5 | 0.5mm | 2.5mm | 2.8mm |
| M4 x 0.7 | 0.7mm | 3.3mm | 3.7mm |
| M5 x 0.8 | 0.8mm | 4.2mm | 4.6mm |
| M6 x 1.0 | 1.0mm | 5.0mm | 5.5mm |
| M8 x 1.25 | 1.25mm | 6.8mm | 7.4mm |
| M10 x 1.5 | 1.5mm | 8.5mm | 9.3mm |
| M12 x 1.75 | 1.75mm | 10.2mm | 11.1mm |
| M14 x 2.0 | 2.0mm | 12.0mm | 13.0mm |
| M16 x 2.0 | 2.0mm | 14.0mm | 15.0mm |
| M20 x 2.5 | 2.5mm | 17.5mm | 18.8mm |
| M24 x 3.0 | 3.0mm | 21.0mm | 22.5mm |
Thread forming taps need a LARGER drill diameter (~85% engagement gives the right thread profile). Most tap manufacturers publish specific drill sizes for their thread-forming range — follow those rather than rule-of-thumb formulas.
For the full chart (metric coarse, metric fine, UNC, UNF, BSW, BSF, BSP, NPT), see Threading & Tap Drill Size Chart.
Tap Material — HSS, HSS-Co, PM-HSS, Carbide
Tap material selection mirrors drill bit material selection but with tighter constraints. Taps work harder than drills (the full tap thread is in contact, not just a cutting edge), so material choice has higher impact on tool life. For deeper coverage of tool material families, see the Cutting Tool Materials Guide.
| Material | Best For | Don't Use For |
|---|---|---|
| HSS (M2) | Mild steel, brass, aluminium hand-tapping. Entry workshop tier. | Stainless (work-hardening), production runs above ~100 holes. |
| HSS-Co 5% (M35) | Stainless 304, harder mild steel (1045), alloy steel. The cobalt content survives the work-hardening cycle. | Cost-sensitive workshop tapping where HSS will do. |
| HSS-Co 8% (M42) | 316 stainless, harder alloy steel, production tapping. Maximum HSS-Co tier. | General mild steel (over-engineered). |
| PM-HSS / HSSE | Premium production work, finer-grain edge holding for difficult-to-machine alloys. Bridges between HSS-Co and solid carbide. | Cost-sensitive low-volume work. |
| Solid carbide | Hardened steel (35-50 HRC), high-production CNC tapping, premium aerospace/automotive applications. | Hand tapping (carbide taps are brittle and shatter under uneven load). |
The single most common tap selection error: using HSS taps on stainless steel. Stainless work-hardens the moment the tap hesitates — HSS doesn't have the hot hardness to survive. The tap glazes, stops cutting, and either snaps or strips. Always use HSS-Co or PM-HSS for stainless.
Tap Coatings — Matching Coating to Material
Tap coatings reduce friction (lower tapping torque), improve heat resistance (longer life in hard materials) and prevent built-up edge (cleaner threads). For full coating coverage, see the Cutting Tool Coatings Guide.
| Coating | Colour | Best For Tapping | Avoid |
|---|---|---|---|
| Bright (uncoated) | Silver | Aluminium, brass, copper, soft non-ferrous — uncoated reduces galling on soft alloys. | Stainless, harder steels. |
| Black oxide / Steam tempered | Black or dark blue | Cost-efficient hand-tap finish for mild steel and general workshop use. | Stainless (negligible performance benefit). |
| TiN — Titanium Nitride | Gold | General-purpose for mild steel, alloy steel, cast iron tapping. | Aluminium (limited benefit). |
| TiCN — Titanium Carbo-Nitride | Grey-blue / blue-violet | Stainless steel tapping — lubricious finish reduces tapping torque significantly. Often the right cobalt-stainless combination. | High-heat dry tapping. |
| TiAlN — Titanium Aluminium Nitride | Black-purple | Hardened steel and high-temperature tapping. Premium tier for production work. | Aluminium (Al-on-Al catalyses). |
| AlCrN | Dark grey | Premium coating for tough alloys and high-volume production. | Cost-sensitive workshop work. |
| Helical (Steam Oxide + Helix) | Black with helical sheen | Premium cobalt tap finish — good for stainless and difficult materials. | Workshop hand tapping where the cost isn't justified. |
The dominant industry combination for stainless production tapping is HSS-Co (M35 or M42) + TiCN coating. For hardened steel, the combination shifts to PM-HSS or solid carbide + TiAlN or AlCrN. For aluminium and brass, uncoated bright HSS is usually correct — coatings add cost without proportional life benefit.
Brands Stocked at AIMS — Honest Selection Guide
AIMS stocks taps and dies from multiple manufacturers. Each brand has a specific strength.
Sutton Tools — Engineering-Grade Across the Full Range
Sutton Tools dominates the AIMS tap and die catalogue. Sutton designs and manufactures in Melbourne, supplies the major Australian engineering, tool-room and CNC production market, and offers the full depth of HSS, HSS-Co (M35 and M42), PM-HSS and coated taps. Sutton's tap catalogue covers:
- Hand taps (metric and imperial, taper/plug/bottoming) — HSS and HSS-Co
- Spiral point (gun) taps — HSS, HSS-Co, TiCN-coated
- Spiral flute taps — HSS, HSS-Co, multiple helix angles
- Thread forming taps — HSS-Co
- Machine nut taps for production tapping
- Premium PM-HSS for difficult materials
For Australian engineering and tool-room work, Sutton is the default. Browse the Sutton Tools collection.
Bordo — Workshop and Specialty Range
Bordo's tap range complements Sutton with workshop-tier HSS hand taps and competitive pricing for general trade and workshop use. Bordo's strength is breadth across the entire workshop catalogue — not just taps but also drills, hole saws, abrasives, masonry — so for tradies who buy a kit, Bordo is the consolidated supplier. Browse the Bordo collection.
Brand Selection Summary
| Application | Recommended Brand | Why |
|---|---|---|
| Production CNC tapping (steel, stainless) | Sutton Tools (spiral point or spiral flute HSS-Co) | Engineering grade, locally manufactured, full M-range plus imperial |
| Aerospace / aluminium thread forming | Sutton Tools (thread forming) | Cold-formed thread strength + chipless production |
| Hardened steel tapping | Sutton solid carbide or PM-HSS (special order) | HSS won't survive — needs the premium tier |
| Workshop general tapping | Bordo or Sutton entry HSS | Both deliver good value at the workshop tier |
| Hand-tapping with a tap wrench | Bordo hand tap set or Sutton hand tap range | Either works — pick by what you already own |
| Heritage thread restoration (BSW/BSF) | Sutton imperial hand taps | Sutton holds the comprehensive BSW/BSF range |
AIMS-Stocked Tap & Die Range Cross-Reference
Direct links to the AIMS tap and die collections. The numbers in brackets are current stock counts.
Threading hub: All threading products (1,083 lines) · Taps (599) · Threading dies (179)
Metric taps:
- Metric Hand Taps (43)
- Metric Spiral Point Taps (70)
- Metric Spiral Flute Taps (80)
- Metric Thread Forming Taps (29)
- Metric Machine Nut Taps (3)
Imperial taps:
- Imperial Hand Taps (63)
- Imperial Spiral Point Taps (37)
- Imperial Spiral Flute Taps (34)
- Imperial Straight Flute Taps (83)
- Imperial Thread Forming Taps (12)
- Imperial Machine Nut Taps (14)
Dies and accessories:
- Threading Dies (179)
- Die Nuts (70 — for thread restoration)
- Tap & Die Sets (85)
- Tap Wrenches (22)
- Die Holders & Stocks (10)
By brand: Sutton Tools · Bordo · Shop by Brand.
Tapping Technique — Hand and Machine
Hand Tapping (Tap Wrench)
- Drill the correct tap drill size (see the tap drill chart) and chamfer the hole top with a countersink or deburring tool.
- Apply cutting fluid (tap magic, soluble oil, or thread cutting compound — see the cutting fluids guide).
- Start the tap square to the work — check with a small engineer's square on two sides.
- Turn forward 1/2 to 1 full turn, then reverse 1/4 turn to break the chip.
- Continue the forward-and-break cycle until the desired depth is reached.
- For blind holes, switch to a bottoming tap to reach the bottom — never force a plug tap deeper.
If the tap seizes or breaks: common causes are wrong drill size (too tight), tap not square to the work, no cutting fluid, or wrong tap type for the material (HSS in stainless). For tap removal techniques after a breakage, the broken-tap-removal articles in the AIMS guides cover the escalation ladder — carbide tap extractor > spark erosion > helicoil/recoil thread repair.
Machine Tapping (Drill Press, Mag Drill, Mill, CNC)
- Spindle speed: roughly 1/2 the equivalent drilling RPM for the same size hole. For small taps (M3-M6) start around 300-500 RPM; for M10-M20 around 100-200 RPM.
- Use a tapping head with floating compensation, or a CNC rigid-tapping cycle that synchronises spindle and feed.
- Coolant or cutting fluid flow at the tap continuously.
- For stainless and harder steels, spiral point or spiral flute is much safer than hand tap — chip evacuation is critical.
- Tap drill diameter same as hand tap chart; thread forming requires manufacturer's larger drill size.
For complete cutting parameters (RPM, feed, surface speed), see the Cutting Speeds & Feeds Reference.
Australian & International Standards Relevant to Taps and Dies
Thread cutting tools and the threads they cut are governed by separate standards:
- ISO 529 — Cutting taps: nomenclature, designation, dimensions. The international reference for tap geometry and naming conventions.
- ISO 261 — General-purpose metric screw threads: thread profile. Defines the M-series thread form.
- ISO 965 — ISO general-purpose metric screw threads: tolerances. Defines 6g/6H thread fits.
- ANSI B1.1 — Unified inch screw threads (UNC, UNF, UNEF). The reference for American thread forms.
- BS 84 — Parallel screw threads of Whitworth form. Heritage Australian and UK BSW/BSF reference.
- ISO 228 — Pipe threads where pressure-tight joints are not made on the threads. The BSP (G-series) parallel pipe thread.
- ISO 7 — Pipe threads where pressure-tight joints are made on the threads. The BSPT (Rc/R) tapered pipe thread.
- ANSI B1.20.1 — Pipe threads, general purpose (inch). The NPT thread reference.
- ISO 4957 — Tool steels: covers M-series HSS designations.
What's NOT a tap or die standard: AS 1442 is sometimes mistakenly cited as a fastener/tool standard — it isn't. AS 1442 is for hot-rolled carbon steel bars (the raw material). It governs steel feedstock, not finished taps or the threads they cut. Don't reference AS 1442 in tap or die purchase specifications.
Tap & Die Selection — Frequently Asked Questions
What's the difference between a hand tap and a machine tap?
Hand taps are designed for use with a hand-driven tap wrench and come as a three-tap progression (taper, plug, bottoming) in the same thread size — taper starts the thread, plug cuts the working portion, bottoming finishes close to the bottom of a blind hole. Machine taps are designed for spindle-driven work (drill press, mag drill, CNC) and include spiral point taps (for through holes) and spiral flute taps (for blind holes). Machine taps cut faster and are usually a single tap rather than a three-step set.
Should I use a spiral point or spiral flute tap?
Spiral point taps (also called gun taps) push chips forward out the bottom of the hole — use them for through holes. Spiral flute taps pull chips backwards up out of the hole — use them for blind holes. Using a spiral point tap in a blind hole packs chips at the bottom and snaps the tap. Using a spiral flute tap in a through hole works but is usually slower than spiral point.
What is a thread forming tap and when do I use it?
Thread forming taps don't cut — they cold-form the thread by displacing material. The result: no chips at all, threads about 30-40% stronger than cut threads (because the grain flows around the thread instead of being severed), and zero chip jamming. Thread forming only works in DUCTILE materials: aluminium, copper alloys, free-machining brass, low-carbon mild steel, austenitic stainless. Cannot be used in cast iron, hardened steel or brittle materials. Requires a slightly larger drill size than cutting taps.
What size drill do I need for an M8 tapping hole?
For an M8 x 1.25 coarse tap (the most common metric M8), drill 6.8mm. For M8 x 1.0 fine pitch, drill 7.0mm. Don't confuse the M-designation with the drill size — M8 means the thread has 8mm major diameter, but the hole you drill is smaller (the tap drill size). Quick formula for metric coarse cutting taps: tap drill = major diameter minus pitch (so M8 - 1.25 = 6.75, rounded to 6.8mm).
What's the difference between BSP and NPT pipe threads?
BSP (British Standard Pipe) and NPT (National Pipe Taper) are NOT interchangeable despite having similar nominal sizes. BSP uses a 55-degree thread angle (Whitworth form); NPT uses 60 degrees. Forcing them together damages both threads and creates a leaking joint. Australia uses BSP/BSPT throughout most plumbing, hydraulics and pneumatics; NPT appears on US-sourced equipment and some American automotive imports. Always confirm which system the parent component uses before ordering.
Can I use a die nut to cut a new external thread?
Die nuts (rethread dies) are designed primarily for cleaning damaged or rusty threads on existing bolts — they have less cutting capability than a full split or button die. You CAN use them to cut a light new thread on soft material in an emergency, but for cutting new threads from raw round stock use a proper split die or button die in a die holder. The split die is workshop standard for hand-threading; the button die is better for production.
Why did my tap break?
Common causes: (1) wrong drill size (too tight — too much torque on the tap), (2) tap not started square to the work, (3) no cutting fluid, (4) wrong tap type (HSS in stainless, or spiral point in a blind hole), (5) chip jamming because the chip wasn't broken regularly during hand tapping, (6) tap blunt from prior overuse. For removal after breakage, the escalation ladder is: tap extractor screws → carbide pin extractor → spark erosion → helicoil or recoil thread repair if the hole is destroyed.
What's the right cutting fluid for tapping?
For steel and stainless: thread cutting compound (paste) or tap magic cutting fluid. For aluminium: kerosene, methylated spirits, or a dedicated aluminium tap lube — don't use general cutting oil on aluminium because it can leave a film that becomes problematic. For brass and bronze: usually dry, or light kerosene. For cast iron: dry — cast iron dust is the lubricant. Coverage in detail: Cutting Fluids Guide.
Are HSS taps OK for stainless steel?
No. Plain HSS does not have the hot hardness to survive stainless steel's work-hardening cycle. The tap glazes within a few threads and either snaps or strips. Always use HSS-Co (M35 5% cobalt or M42 8% cobalt) for stainless, or premium PM-HSS for production work. Combine with a TiCN coating for best results — the lubricious coating reduces tapping torque significantly.
What thread system is on Australian water and gas plumbing?
Australian plumbing uses primarily BSP (British Standard Pipe, G-series parallel) and BSPT (British Standard Pipe Tapered, Rc/R-series). Water lines and pneumatic lines typically use BSP parallel with separate sealing washers or PTFE tape. Gas and pressure-tight plumbing typically uses BSPT tapered threads with thread sealant. NPT (American National Pipe Taper) is NOT standard in Australian plumbing — only appears on imported US equipment.
How do I know if a thread is BSW or UNC?
Both have similar nominal diameters (e.g. 3/8 inch) but different angles and pitches. BSW (British Standard Whitworth) has a 55-degree thread angle and Whitworth-specific pitches (3/8 BSW = 16 TPI). UNC (Unified National Coarse) has a 60-degree angle and Unified pitches (3/8 UNC = 16 TPI). Both happen to have 16 TPI at 3/8 — but the angle mismatch means they cross-thread if forced together. Identify the thread by measuring TPI carefully and checking the angle, or check the parent fastener stamping. Heritage Australian equipment is usually BSW/BSF; US-imported automotive is UNC/UNF.
Can a broken tap be removed without damaging the part?
Sometimes. The escalation ladder for broken tap removal: (1) try tap extractor screws — screw-in tool that engages the tap flutes from the open end and lets you back the tap out, (2) carbide pin punch — drive carbide pins down the flute slots to break the tap into pieces, (3) spark erosion (EDM) — the most reliable but requires sending to a specialist with EDM equipment, (4) accept the loss and helicoil/recoil thread repair — drill out the original thread and insert a thread repair coil. Soft mild steel and aluminium are most recoverable; hardened steel is the hardest.
What's the cost difference between HSS and HSS-Co taps?
HSS-Co taps typically cost 50-100% more than equivalent HSS taps. The premium is justified the moment you tap stainless steel or harder alloys — HSS-Co's cobalt content retains hardness at the cutting temperatures that destroy plain HSS edges. For workshop mild-steel tapping, HSS is fine. For stainless and production work, HSS-Co's tool life advantage makes it cheaper per hole despite the higher purchase price.
Is metric coarse or metric fine the right choice?
Metric coarse (M-series) is the default for general engineering, structural fasteners, machinery, automotive and most construction work. Metric fine (e.g. M8 x 1.0 instead of M8 x 1.25) is used where you need: finer adjustment, higher resistance to vibration loosening (more turns per unit length = more friction grip), or higher tensile load capacity in harder materials. Aerospace, precision instruments and some automotive applications use metric fine. Most workshops stock metric coarse only and source metric fine on specific need.
Does AIMS stock metric fine taps?
Yes — Sutton Tools and Bordo both produce metric fine taps in standard sizes (M6 x 0.75, M8 x 1.0, M10 x 1.25, M12 x 1.5, etc.). For less common sizes or specialty applications, AIMS can source by special order — ring (02) 9773 0122. The base metric range AIMS stocks covers metric coarse comprehensively; fine pitches and specialty thread forms (ACME, trapezoidal) typically come from special-order Sutton inventory.
Related AIMS Industrial Reference Material
For deeper coverage of the engineering concepts behind tap and die selection, see:
- Threading & Tap Drill Size Chart — complete tap drill sizes for metric coarse, metric fine, UNC, UNF, BSW, BSF, BSP, NPT
- Tap Types Explained — in-depth coverage of taper/plug/bottoming/spiral point/spiral flute/forming taps
- Workpiece Material Cross-Reference Chart — SAE/AISI/DIN/JIS/AS/NZS equivalents
- Cutting Speeds & Feeds Reference — RPM, feed rate and cutting parameter tables
- Cutting Tool Materials Guide — HSS, HSS-Co, PM-HSS, solid carbide
- Cutting Tool Coatings Guide — TiN, TiCN, TiAlN, AlCrN explained
- Cutting Tool Troubleshooting Guide — tap failure diagnosis
- Metric to Imperial Conversion Chart
- Drill Bit Selection Guide — pair with tap drill sizing
- Cutting Fluids & Cutting Oils Guide
- Tap Magic Cutting Fluids
- Recoil Thread Repair Cross-Reference — for when a tap has done its damage
For tap, die, or threading purchase advice, or to source items we don't currently list, ring AIMS Industrial on (02) 9773 0122 or use the contact page. Trade accounts and bulk pricing available.