Spiral Point (Gun Tap) vs. Spiral Flute Tap Chart & Selection Guide
Choose a Spiral Point Tap ("Gun Tap", DIN 2181 Form B) for through-holes: its angled front shear grind shoots chips forward ahead of the tap, allowing a shallow, rigid flute core for high-speed CNC tapping. Choose a Spiral Flute Tap (DIN Form C/E, 15°–50° helix) for blind holes: its helical flutes auger chips upward and out of the hole entrance.
Spiral Point (Gun Tap) vs. Spiral Flute Tap Geometry, Helix Angle & Chamfer Selector
Select hole geometry, workpiece alloy, and thread pitch to prescribe the exact tap flute geometry, DIN 2181 chamfer form, and bottoming Z-clearance.
The Chip Evacuation Mechanics of Spiral Point ("Gun") Taps vs. Spiral Flute Taps
In CNC rigid tapping cycles (G84), over 85% of broken taps are caused not by dull cutting edges, but by chip jamming inside the flute gullets. Standard straight-flute hand taps have zero axial helix; they merely trap sheared metal ribbons inside their flutes, making them suitable only for short-chipping gray cast iron or manual maintenance re-chasing. Production machine shops rely on two engineered chip-directing geometries standardized under ISO International Metrology Standard (ISO 529), DIN 2181, and ASME Geometric & Mechanical Standards (ASME B94.9).
Despite its name, a Spiral Point Tap (Gun Tap — DIN Form B) has straight flutes along its body; the "spiral" is an angular shear grind (12° to 15°) ground into the first 4 to 5 chamfer threads at the nose. As the tap rotates clockwise, this angular point curls and shoots chips forward ahead of the tool like a rifle barrel ("gun tap"). Because chips exit out the bottom of the through-hole rather than traveling up the flutes, the flute gullets can be made shallow—giving a gun tap a thick, torsionally rigid central web that withstands 30% higher cutting speeds (SFM) than spiral flute taps.
Conversely, Spiral Flute Taps (Helical Taps — DIN Form C & E) are ground with continuous right-hand helical flutes (from 15° low-helix for hardened steel up to 45°–50° high-helix for stringy 304/316 stainless steel and 6061 aluminum). Acting like a twist drill, a spiral flute tap pulls chips upward against gravity and ejects them out the top of the hole, making it mandatory for blind holes where forward-pushed chips would pack against the bottom drill cone and snap the tap on spindle reversal, as verified in NIST (National Institute of Standards and Technology) shop trials.
| Tap Geometry Style | DIN Chamfer Form | Helix / Point Angle | Chip Evacuation Direction | Ideal Hole Geometry | Core Web Strength & Torque |
|---|---|---|---|---|---|
| Spiral Point (Gun Tap) | Form B (4.0–5.0 Pitches) | 0° Flute + 12°–15° Shear Point | Forward (Shoots chips ahead) | Through-holes & deep clearance blind holes | Thick web; highest cutting tap rigidity & speed |
| 15° Low-Helix Spiral Flute | Form C (2.0–3.0 Pitches) | 15°–25° Right-Hand Helix | Upward / Backward | Blind holes up to 1.5×D in hard steel / Ti | Strong tooth support against chipping in 35–45 HRC |
| 35° Medium Spiral Flute | Form C (2.0–3.0 Pitches) | 35° Right-Hand Helix | Upward / Backward | Blind holes up to 2.0×D in carbon & alloy steel | Balanced core strength & smooth upward chip lift |
| 45°–50° High-Helix Spiral Flute | Form C / E (1.5–2.5 Pitches) | 45°–50° Right-Hand Helix | Aggressive Upward Lift | Deep blind holes (2.5×D) in 304/316 SS & 6061 Al | Thinner web; prevents stringy birdnesting at bottom |
| Straight Flute Hand Tap | Form A/C/E (Taper/Plug/Bottom) | 0° Straight Flute | Trapped inside flute gullets | Cast iron, brass & manual maintenance | Zero axial chip lift; requires pecking in deep holes |
| Fluteless Roll-Form Tap | Form C / E (Lobe Lead) | Chip-Free Forming Lobes | Zero Chips (Plastic Flow) | Through & blind holes in ductile metals (≥10% elong.) | Solid core (3× stronger); requires larger pre-drill |
Decoding DIN 2181 Tap Chamfer Lead Forms (Form A, B, C, D, and E)
Selecting the correct flute helix must be paired with the proper chamfer lead length (the tapered nose teeth that progressively shear the thread profile to full depth) as documented in Machinery's Handbook (Industrial Press). A longer chamfer (Form B, 4–5 pitches) distributes the cutting load across 12 to 20 teeth for long tool life, whereas a short bottoming chamfer (Form E, 1.5–2 pitches) concentrates the entire metal removal load onto just 4 to 6 teeth.
Furthermore, matching surface coating and neck relief to the workpiece alloy prevents cold-welding (galling) on the reversal stroke: steam-oxide (OX) or TiCN coatings retain extreme-pressure cutting fluid in austenitic stainless steel, whereas bright un-coated or DLC-coated high-helix taps prevent built-up edge in 6061-T6 aluminum. Always verify your bottoming Z-clearance and synchronized feed rate on our Blind Hole Tap Depth Calculator, G84 Rigid Tapping Feed & Speed Calculator, Roll Form Tap Drill Chart, and Master Tap Drill Chart.
| DIN 2181 Form | US ANSI Equivalent | Incomplete Lead Threads | Chamfer Angle per Side | Chip Load per Chamfer Tooth | Min Blind-Hole Bottom Clearance |
|---|---|---|---|---|---|
| Form A | Taper Tap | 6.0 to 8.0 Pitches | 4° – 5° | Very Light (12%–16% per tooth) | 8.0 × Pitch + Drill Cone (Through-Hole Only) |
| Form B | Spiral Point Plug Tap | 3.5 to 5.0 Pitches | 6° – 8° + Gun Grind | Moderate (20%–28% per tooth) | 5.5 × Pitch + Chip Pocket + Drill Cone |
| Form D | Modified Plug Tap | 3.5 to 5.0 Pitches | 6° – 8° | Moderate (20%–28% per tooth) | 4.5 × Pitch + Drill Cone |
| Form C | Semi-Bottoming / Short Plug | 2.0 to 3.0 Pitches | 10° – 12° | Heavy (33%–50% per tooth) | 2.5 × Pitch + Drill Cone (CNC Blind Standard) |
| Form E | True Bottoming Tap | 1.5 to 2.0 Pitches | 15° – 18° | Extreme (50%–65% per tooth) | 1.5 × Pitch + Flat-Bottom End Mill Bore |