Imperial Spiral Flute Taps

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.

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.