AMSUO Spiral-Flute Taps — HSS-E Cobalt, TiCN Coated, UNC/UNF Inch Series, for Blind Holes

Pull chips backwards out of blind holes

Spiral-flute taps lift the chip back up and out of the hole as they cut, so a blind hole never fills with packed chips. You get full thread depth all the way down, and you keep the threads and the tap out of harm's way.

Why it works

The flutes are milled on a helix instead of straight. Turning clockwise, the cutting edges carry the chip up the helix and out of the hole — the opposite direction from a spiral-point tap. That makes these the standard choice for blind holes, where a forward-driven chip has nowhere to go.

• Best for: blind holes, threaded holes that must bottom out, holes with no exit
• Not for: very deep holes where chip evacuation is limited; use a spiral-point tap in a through hole instead
• Thread forms: UNC and UNF inch series, right hand

Material and coating

HSS-E (cobalt high-speed steel) — resists softening at cutting temperature, which is the main failure mode when a tap cannot be cleared often.

TiCN coating (violet-grey) — titanium carbonitride is harder and more wear-resistant than TiN, making it the usual choice for stainless steel and harder alloys where edge wear drives tap life.

Chamfer type — pick by hole bottom

Plug chamfer — the general-purpose lead. Easier to start and easier to turn, but it will not thread as close to the bottom of the hole.

Bottoming chamfer — a shorter lead that cuts threads closest to the bottom of a blind hole. Start the hole with a plug or taper tap, then finish with the bottoming tap.

Size range and recommended tap drill

Tap drill sizes above are the standard published values for approximately 75% thread engagement. Flute count runs 2 to 3 depending on thread size. Pitch diameter limit is standard inch-series fit (H2 class). Other thread sizes, left-hand threads, and metric series are available on request.

Related tooling

Prepare the hole — drill to the recommended tap drill depth, allowing extra depth for the chip to collect below the last full thread.

Hold the tap — use a tap wrench matched to the shank and square drive end.

Keep it square — a tap guide keeps the tap perpendicular while the first threads are formed.

For use on

Steel, stainless steel, cast iron, aluminum, brass, bronze, copper, and most plastics.