Imperial Straight Flute Taps

Imperial straight flute taps cut threads in the inch-based thread forms still common in Australian plumbing, automotive, mining and older industrial machinery. Straight flute is the original, general-purpose tap geometry — chips collect in the flutes, the operator reverses to break them, then continues. Slower than spiral-point or spiral-flute taps for production work, but well-suited to hand tapping and short blind holes in steel, brass and cast iron.

AIMS stocks 83 imperial straight flute taps across BSW, BSF, UNC, UNF, UNEF, UN and BA thread forms in HSS, primarily from Sutton (Australian-made) and Goliath.

Imperial Straight Flute Tap Selection — Quick Reference

Imperial straight flute taps cut inch-based threads still common in AU plumbing + automotive + mining + older machinery. General-purpose tap geometry — chips collect in flutes, operator reverses to break. Slower than spiral-point/flute for production but well-suited to hand tapping + mixed materials.

Critical: Match tap drill size to thread — see threading tap size chart. Use cutting fluid + back off ¼ turn every full turn to break chips. NEVER force a stuck tap — broken taps in steel are very difficult to remove. Brands: Sutton Tools, Bordo. Companion: all taps, threading, tap wrenches.

Imperial Thread Forms Stocked

• BSW (British Standard Whitworth) — 55° flank angle, coarse pitch. Still used in older British machinery, plumbing fittings and some Australian heritage applications.
• BSF (British Standard Fine) — 55° flank angle, fine pitch. Companion to BSW where higher clamp force or vibration resistance is needed.
• UNC (Unified Coarse) — 60° flank angle, coarse pitch. The North American imperial standard, common in imported machinery, automotive and general fastening.
• UNF (Unified Fine) — 60° flank angle, fine pitch. Aerospace, automotive, precision assemblies.
• UNEF (Unified Extra Fine) — Very fine pitch. Thin-wall tubing, instrumentation.
• UN (Unified Constant Pitch) — Special-pitch threads for specific applications.
• BA (British Association) — Small instrument and electrical threads.

If you need to match a thread you've measured, the Tap Size Chart and our Metric vs Imperial Fasteners Guide will help you confirm which standard and pitch you're looking at.

Taper, Intermediate, Bottoming — Which Do You Need?

Straight flute taps come in three lead styles (also called "chamfers" or "starts"):

• Taper tap (1st tap) — Long lead, 8-10 thread chamfer. Easiest to start; used to begin a thread, especially in tough material or by hand. Through-hole capable but won't thread the full depth of a blind hole.
• Intermediate tap (2nd tap, also "plug tap") — Medium lead, 3-5 thread chamfer. The all-purpose tap for through holes. Most workshops keep this one as a default.
• Bottoming tap (3rd tap) — Short lead, 1-2 thread chamfer. Threads close to the bottom of a blind hole. Used after a taper or intermediate has done the initial work.

For a deeper walkthrough of tap selection, hand-tapping technique, lubrication and broken-tap recovery, see our full Tap and Die Guide.

Sutton vs Goliath — Which Brand?

Sutton Tools — Australian manufacturer based in Melbourne since 1917. The T-series codes (T414, T415, T446, T451, etc.) cover most imperial straight flute combinations. Premium HSS grade, ground threads, made-here quality.

Goliath — UK heritage brand, also HSS construction. Often available in sizes Sutton doesn't catalogue, including some left-hand and larger-diameter imperial taps. Strong choice for restoration and heritage machinery work.

Tapping Drill Sizes and Cutting Fluid

Every imperial tap needs a specific tapping drill diameter — too small and the tap labours; too big and the thread strips. Our Tap Size Chart covers tapping drill sizes for BSW, BSF, UNC, UNF and BSP in one reference.

Cutting fluid extends tap life dramatically. For practical fluid selection by material and operation, see the Cutting Fluids Guide.

Sister Tap Collections

Other imperial tap styles stocked at AIMS:

• Imperial Hand Taps — traditional 3-piece sets for hand tapping.
• Imperial Spiral Point Taps — "gun taps" for through-hole tapping with forward chip ejection.
• Imperial Spiral Flute Taps — for blind holes, chips ejected backwards.
• Imperial Machine Nut Taps — long-shank taps for production nut manufacture.
• Imperial Thread Forming Taps — cold-forming for ductile materials, no chips produced.

For the full threading range including metric taps, dies and accessories, see the parent Threading collection.

Common Questions

What's the difference between a straight flute tap and a hand tap? "Hand tap" usually refers to a 3-piece set (taper + intermediate + bottoming) intended for manual tapping with a tap wrench. Most straight flute taps are also hand taps — the term overlaps. We split them into separate collections at AIMS because some customers shop by tap geometry (straight flute) and others by intended use (hand tapping sets).

Can I use a straight flute tap in a machine? Yes — straight flute taps can be used in tapping heads, drill presses and CNC machines, but they're slower than spiral-point or spiral-flute taps because chip evacuation is poorer. For production tapping in machines, the spiral-flute or spiral-point variants are better.

Why are imperial taps so expensive in larger sizes? Imperial straight flute taps above 1" (25mm) require a lot more HSS bar stock and machining time than metric equivalents — there are fewer Australian manufacturers making them, so prices reflect both material and limited supply.

Do you stock left-hand imperial straight flute taps? Yes — selected sizes in the Sutton T-series and Goliath ranges. Search the collection for "left hand" or call us if the size you need isn't visible.

Need a specific size, pitch or thread standard that's not showing? Call the Sydney team on (02) 9773 0122 — we hold a wider range than the online catalogue shows and source non-stock sizes from Sutton and Goliath direct.