What RPM for a M20x2.5 tap?

RPM = 3.82 × SFM ÷ D with D = 0.79 in. With a general-purpose HSS tap that is about 340 RPM in 6061 aluminum (70 SFM) and 100 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 M20x2.5 tap?

Feed per revolution equals the pitch: 2.5 mm. Feed (mm/min) = RPM × 2.5, so at 340 RPM the feed is 850 mm/min.

How fast can I run a M20x2.5 form (roll) tap?

OSG lists 65–115 SFM for form taps in aluminum alloys, which is 320–560 RPM for M20x2.5. Form taps need a larger hole: about 18.90 mm (18.90 mm).

What speed for a M20x2.5 tap in stainless steel?

General-purpose HSS taps: 10–20 SFM, or 50–100 RPM at 125–250 mm/min. Keep the tap cutting and use 60–65% thread to cut torque.

M20x2.5 tap speeds and feeds

A M20x2.5 tap feeds one pitch per turn: 2.5 mm per rev. With a general-purpose HSS tap, start near 340 RPM and 850 mm/min in 6061 aluminum, or 100 RPM and 250 mm/min in mild steel.

ISO metric coarse thread · major Ø 20.00 mm · tap drill 17.5mm (17.50 mm) for a cut tap, 18.90 mm for a form tap.

M20x2.5 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.

M20x2.5 cut and form tap speeds
Material	Cut SFM	Cut RPM	Cut mm/min	Form SFM	Form RPM	Form mm/min
Aluminum 6061 / 7075	70–90	340–440	850–1,100	65–115	320–560	800–1,400
Free-machining / mild steel (12L14, 1018)	20–40	100–190	250–475	50–115	240–560	600–1,400
4140 alloy steel (annealed to <35 HRC)	20–30	100–150	250–375	50–85	240–410	600–1,025
304 / 316 stainless	10–20	50–100	125–250	15–40	70–190	175–475
Tool steel (A2, D2, O1, H13, P20)	15–25	70–120	175–300	8–25	40–120	100–300
Gray / ductile cast iron	15–30	70–150	175–375	Not listed	Not listed	Not listed
Brass / bronze	60–100	290–490	725–1,225	Not listed	Not listed	Not listed
Titanium (6Al-4V, CP)	5–15	20–70	50–175	8–15	40–70	100–175
Plastics and composites (acetal, nylon, G-10)	50–70	240–340	600–850	Not listed	Not listed	Not 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.

M20x2.5 premium cut tap speeds (OSG)
Material	OSG row	SFM	RPM	mm/min
Aluminum 6061 / 7075	Aluminum alloys	70–120	340–580	850–1,450
Free-machining / mild steel (12L14, 1018)	Carbon steels <35 HRC	80–120	390–580	975–1,450
4140 alloy steel (annealed to <35 HRC)	Alloy steels <35 HRC	35–65	170–320	425–800
304 / 316 stainless	Stainless 300 & 400 series <35 HRC	15–75	70–360	175–900
Tool steel (A2, D2, O1, H13, P20)	Alloy, tool & die steels 30–40 HRC	15–30	70–150	175–375
Gray / ductile cast iron	Cast iron	50–120	240–580	600–1,450
Titanium (6Al-4V, CP)	Titanium alloys <35 HRC	15–20	70–100	175–250

Worked example: M20x2.5 in 6061 aluminum

Surface speed: 70 SFM (low end of 70–90 for a general-purpose HSS tap).
RPM = 3.82 × SFM ÷ D = 3.82 × 70 ÷ 0.79 ≈ 340 RPM (D = 20 mm = 0.79 in; or RPM = 1000 × 21.3 m/min ÷ (π × 20)).
Feed per rev = pitch = 2.5 mm.
Feed = RPM × pitch = 340 × 2.5 = 850 mm/min (33.5 IPM).

G84 tapping code for M20x2.5

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

Fanuc rigid tap (M29)

(M20x2.5 TAP - RIGID)
G21 G17 G40 G80 G90
T5 M06
G54 G00 X0. Y0.
G43 H05 Z25. M08
M29 S340           (RIGID TAP MODE; M-CODE SET BY PARAMETER)
G98 G84 Z-30. R3. F850.
G80 M09
G91 G28 Z0.
M30

Haas rigid tap

G21 G00 G90 G54 X0. Y0.
G43 H05 Z3. M08
G84 Z-30. R3. F850. S340   (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 S340) and the same F850 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 M20x2.5-LH taps use G74 instead of G84.
If the control caps rigid-tap RPM, lower S and recompute F: F = S × 2.5.

Notes for this size

M20x2.5 needs real torque: check that your spindle makes enough torque at 100 RPM (a gear-range spindle may need its low range). Thread milling is often the safer choice in tough material at this size.
A 2.5 mm pitch is coarse: the axis moves 2.5 mm every revolution, so check the machine can hold sync at the IPM shown before raising RPM.

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 M20x2.5

Tap drill, cut tap 75%: 17.5mm (17.50 mm) · 17.5mm drill size and speeds
Form tap drill (65%): 18.90 mm (18.90 mm)
50% thread drill for hard or gummy stock: 18.5mm (18.50 mm)

Tap calculator, prefilled for M20x2.5 M20x2.5 tap drill size Tap drill chart

Common questions

What RPM for a M20x2.5 tap?: RPM = 3.82 × SFM ÷ D with D = 0.79 in. With a general-purpose HSS tap that is about 340 RPM in 6061 aluminum (70 SFM) and 100 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 M20x2.5 tap?: Feed per revolution equals the pitch: 2.5 mm. Feed (mm/min) = RPM × 2.5, so at 340 RPM the feed is 850 mm/min.
How fast can I run a M20x2.5 form (roll) tap?: OSG lists 65–115 SFM for form taps in aluminum alloys, which is 320–560 RPM for M20x2.5. Form taps need a larger hole: about 18.90 mm (18.90 mm).
What speed for a M20x2.5 tap in stainless steel?: General-purpose HSS taps: 10–20 SFM, or 50–100 RPM at 125–250 mm/min. Keep the tap cutting and use 60–65% thread to cut torque.

Nearby sizes

Sources

Productivity Inc. tool catalog, Tech Info - Taps: General Purpose & Other Tap Speeds (pp. 405-416)
OSG USA, A Brand & Premium Tooling Recommendation Guide Vol. 4 (Threading and Drilling), EDP 800313CA-V4, 2026
Haas Automation, G84 Tapping Canned Cycle (Group 09), mill G-code reference
Thread dimensions and tap drills: Machinery's Handbook, 31st ed.; ASME B1.1 Unified Inch Screw Threads.

SFM ranges are copied from the tables above; RPM and feed are computed for M20x2.5 (D = 20 mm). Speeds are starting values: your tap maker's data, coolant and machine come first.

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