Buy Imperial Spiral Flute Taps Online in Australia
Imperial spiral flute taps cut threads in blind holes — where the bottom of the hole is closed and chips can't be ejected forward. The helical flutes (typically 30-45° helix) act like a screw conveyor, pulling chips back up and out of the hole as the tap advances.
Spiral flute taps are the right choice for any blind-hole tapping in a machine. They also work in through-holes but are slower than spiral point taps in that role.
Imperial Spiral Flute Tap Sizes — Quick Reference
Imperial spiral flute taps cut threads in BLIND HOLES — where the closed bottom prevents chip ejection forward. The helical flutes (30-45° helix) act as a screw conveyor, pulling chips back up + out of the hole as the tap advances. Use for blind-hole tapping in CNC + machine drives. For through-holes, spiral POINT taps are faster.
| Thread Form | Common Workshop Sizes | Tap Drill Sizes | Best For |
|---|---|---|---|
| UNC (Unified Coarse) | 1/4"-20, 5/16"-18, 3/8"-16, 7/16"-14, 1/2"-13 | #7 / F / 5/16" / U / 27/64" | US-origin machinery, automotive imports, older equipment |
| UNF (Unified Fine) | 1/4"-28, 5/16"-24, 3/8"-24, 7/16"-20, 1/2"-20 | #3 / I / Q / 25/64" / 29/64" | Aerospace, precision automotive, fine-pitch applications |
| BSP (Pipe Thread) | 1/8"-28, 1/4"-19, 3/8"-19, 1/2"-14, 3/4"-14 | per pitch (see size chart) | Pipe threads — sealing thread applications |
| BSW (Whitworth) | 1/4", 5/16", 3/8", 1/2", 5/8", 3/4" | per pitch (see size chart) | Older Australian/UK machinery, vintage equipment |
For tap drill sizes by thread form, see our threading tap size chart. For metric equivalents, see metric spiral flute taps. For through-holes, use spiral point taps (faster). For manual hand tapping, use imperial hand taps.
When to Use a Spiral Flute Tap
- Blind-hole tapping in CNC mills, CNC lathes, tapping heads and drill presses.
- Tapping in aluminium, copper and other ductile materials where stringy chips would jam a spiral point tap.
- Deep tapping where chip evacuation is critical.
Thread Forms Stocked
BSW, BSF, UNC, UNF and selected UNEF sizes — Sutton T-series and Goliath HSS. Australian-made Sutton stocked across most common sizes; Goliath fills gaps including some larger diameters.
Tapping Speeds and Lubrication
Spiral flute taps run a little slower than spiral point in steel — typically 60-80% of spiral point speed in the same material. Compensate with good cutting fluid (flood preferred), proper tapping drill size (see the Tap Size Chart), and a rigid setup.
Aluminium tapping benefits from a fluid that prevents chip welding — see the Cutting Fluids Guide for material-specific recommendations.
Sister Tap Collections
Imperial Straight Flute Taps, Imperial Hand Taps, Imperial Spiral Point Taps (through holes), Imperial Thread Forming Taps, Imperial Machine Nut Taps. Parent: Threading.
Common Questions
Spiral flute or spiral point — what's the rule? Spiral flute for blind holes, spiral point for through holes. If you only have one tap and the hole is unknown, spiral flute is the safer choice — it'll work in both, just slower in through-holes.
Will a spiral flute tap break easier than a straight flute? In tough material, yes — the helical flutes leave less core material in the tap body. Don't push spiral flute taps in hardened steel; use a straight flute or a thread-forming tap instead.
What helix angle should I use? ~30° for general steel work; 40-45° for aluminium and ductile materials where chips are long and stringy.
How deep can I tap a blind hole? A bottoming spiral flute tap reaches within 1-2 threads of the hole bottom. Don't tap into the bottom corner — the radius will damage the tap. Drill at least 3-4 threads deeper than the thread depth required.
Need a specific BSW or UNC size not online? Call (02) 9773 0122 — we hold more than the website lists.