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 — 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
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.
