M8x1.25 tap speeds and feeds

    A M8x1.25 tap feeds one pitch per turn: 1.25 mm per rev. With a general-purpose HSS tap, start near 850 RPM and 1,063 mm/min in 6061 aluminum, or 240 RPM and 300 mm/min in mild steel.

    ISO metric coarse thread · major Ø 8.00 mm · tap drill 6.8mm (6.80 mm) for a cut tap, 7.45 mm for a form tap.

    M8x1.25 tapping speeds by material

    Cut tap = general-purpose HSS tap. Form tap = OSG form (roll) taps. RPM rounded to 10; feed in mm/min = RPM × pitch. Start at the low end.

    M8x1.25 cut and form tap speeds
    MaterialCut SFMCut RPMCut mm/minForm SFMForm RPMForm mm/min
    Aluminum 6061 / 707570–90850–1,0901,063–1,36365–115790–1,390987–1,738
    Free-machining / mild steel (12L14, 1018)20–40240–490300–61350–115610–1,390763–1,738
    4140 alloy steel (annealed to <35 HRC)20–30240–360300–45050–85610–1,030763–1,288
    304 / 316 stainless10–20120–240150–30015–40180–490225–613
    Tool steel (A2, D2, O1, H13, P20)15–25180–300225–3758–25100–300125–375
    Gray / ductile cast iron15–30180–360225–450Not listedNot listedNot listed
    Brass / bronze60–100730–1,210913–1,513Not listedNot listedNot listed
    Titanium (6Al-4V, CP)5–1560–18075–2258–15100–180125–225
    Plastics and composites (acetal, nylon, G-10)50–70610–850763–1,063Not listedNot listedNot listed

    Not listed = no form-tap value in the cited tables (OSG lists no form tap for cast iron; brass and plastics are not in its form-tap table).

    Premium coated cut taps on a rigid CNC

    OSG's starting speeds for its premium HSS-E cut taps (A-Tap family and the titanium/stainless taps it names) are higher than the general-purpose row. Use them only with that class of tap and rigid tapping.

    M8x1.25 premium cut tap speeds (OSG)
    MaterialOSG rowSFMRPMmm/min
    Aluminum 6061 / 7075Aluminum alloys70–120850–1,4601,063–1,825
    Free-machining / mild steel (12L14, 1018)Carbon steels <35 HRC80–120970–1,4601,213–1,825
    4140 alloy steel (annealed to <35 HRC)Alloy steels <35 HRC35–65420–790525–987
    304 / 316 stainlessStainless 300 & 400 series <35 HRC15–75180–910225–1,138
    Tool steel (A2, D2, O1, H13, P20)Alloy, tool & die steels 30–40 HRC15–30180–360225–450
    Gray / ductile cast ironCast iron50–120610–1,460763–1,825
    Titanium (6Al-4V, CP)Titanium alloys <35 HRC15–20180–240225–300

    Worked example: M8x1.25 in 6061 aluminum

    1. Surface speed: 70 SFM (low end of 70–90 for a general-purpose HSS tap).
    2. RPM = 3.82 × SFM ÷ D = 3.82 × 70 ÷ 0.31 ≈ 850 RPM (D = 8 mm = 0.31 in; or RPM = 1000 × 21.3 m/min ÷ (π × 8)).
    3. Feed per rev = pitch = 1.25 mm.
    4. Feed = RPM × pitch = 850 × 1.25 = 1,063 mm/min (41.8 IPM).

    G84 tapping code for M8x1.25

    Rigid tapping, aluminum numbers from the example, metric (G21), depth 1.5 × D. Check your control's manual before running.

    Fanuc rigid tap (M29)

    (M8x1.25 TAP - RIGID)
G21 G17 G40 G80 G90
T5 M06
G54 G00 X0. Y0.
G43 H05 Z25. M08
M29 S850           (RIGID TAP MODE; M-CODE SET BY PARAMETER)
G98 G84 Z-12. R3. F1063.
G80 M09
G91 G28 Z0.
M30

    Haas rigid tap

    G21 G00 G90 G54 X0. Y0.
G43 H05 Z3. M08
G84 Z-12. R3. F1063. S850   (NO M03 NEEDED)
(PECK: ADD Q = PECK DEPTH; J2 = RETRACT 2X, SEE SETTING 130)
G80 G00 Z25. M09

    Floating / tension-compression holder

    Without rigid tapping, run G84 with the spindle on (M03 S850) and the same F1063 feed, but hold the tap in a tension-compression holder: it absorbs the overrun when the spindle stops and reverses. Leave the holder room to float at the bottom, so program the depth a little short and follow the holder maker's setting.

    • Peck tapping (Q) clears chips in deep or blind holes in stainless and 4140; skip it in aluminum unless chips pack.
    • Left-hand M8x1.25-LH taps use G74 instead of G84.
    • If the control caps rigid-tap RPM, lower S and recompute F: F = S × 1.25.

    Notes for this size

    • M8x1.25 is in the size range most shops rigid tap every day. Run the low end of the table first, then raise speed in 10% steps while watching spindle load on the reversal.
    4140 alloy steel (annealed to <35 HRC)
    Prehardened 4140 (28–32 HRC) is at the top of this band: use the low end and 50–65% thread.
    304 / 316 stainless
    Work-hardens: never let the tap dwell or rub, and use a tap made for stainless. 60–65% thread cuts torque sharply.
    Tool steel (A2, D2, O1, H13, P20)
    Values are for annealed or prehardened stock. Tap before heat treat whenever you can; hardened tool steel needs a thread mill or a carbide tap.

    Hole and tools for M8x1.25

    Tap calculator, prefilled for M8x1.25M8x1.25 tap drill sizeTap drill chart

    Common questions

    What RPM for a M8x1.25 tap?
    RPM = 3.82 × SFM ÷ D with D = 0.31 in. With a general-purpose HSS tap that is about 850 RPM in 6061 aluminum (70 SFM) and 240 RPM in mild steel (20 SFM). Premium coated taps on a rigid CNC can run faster; see the second table.
    What is the feed rate for a M8x1.25 tap?
    Feed per revolution equals the pitch: 1.25 mm. Feed (mm/min) = RPM × 1.25, so at 850 RPM the feed is 1,063 mm/min.
    How fast can I run a M8x1.25 form (roll) tap?
    OSG lists 65–115 SFM for form taps in aluminum alloys, which is 790–1,390 RPM for M8x1.25. Form taps need a larger hole: about 7.45 mm (7.45 mm).
    What speed for a M8x1.25 tap in stainless steel?
    General-purpose HSS taps: 10–20 SFM, or 120–240 RPM at 150–300 mm/min. Keep the tap cutting and use 60–65% thread to cut torque.

    Nearby sizes

    Sources

    SFM ranges are copied from the tables above; RPM and feed are computed for M8x1.25 (D = 8 mm). Speeds are starting values: your tap maker's data, coolant and machine come first.

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