Metric Thread Pitch Chart (M1 to M36)

ISO metric threads are named by an M, the nominal diameter in millimetres and, for fine threads, the pitch: M8 on its own means the coarse M8 x 1.25, and M8 x 1 is the fine version. This chart lists 36 common coarse and fine threads from M1 to M36 with the pitch, the basic pitch and minor diameters, the tensile stress area and the tap drill. All values are computed from the ISO 68-1 basic profile, so the arithmetic is shown under the chart. Click a heading to sort.

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Thread	Series	Pitch (mm)	Pitch dia (mm)	Minor dia, nut (mm)	Stress area (mm²)	Tap drill	Thread %
M1 x 0.25	coarse	0.25	0.838	0.729	0.5	0.75 mm	77%
M1.2 x 0.25	coarse	0.25	1.038	0.929	0.7	0.95 mm	77%
M1.6 x 0.35	coarse	0.35	1.373	1.221	1.3	1.25 mm	77%
M2 x 0.4	coarse	0.4	1.740	1.567	2.1	1.6 mm	77%
M2.5 x 0.45	coarse	0.45	2.208	2.013	3.4	2.05 mm	77%
M3 x 0.5	coarse	0.5	2.675	2.459	5.0	2.5 mm	77%
M3.5 x 0.6	coarse	0.6	3.110	2.850	6.8	2.9 mm	77%
M4 x 0.7	coarse	0.7	3.545	3.242	8.8	3.3 mm	77%
M5 x 0.8	coarse	0.8	4.480	4.134	14.2	4.2 mm	77%
M6 x 1	coarse	1	5.350	4.917	20.1	5 mm	77%
M8 x 1.25	coarse	1.25	7.188	6.647	36.6	6.75 mm	77%
M8 x 1	fine	1	7.350	6.917	39.2	7 mm	77%
M10 x 1.5	coarse	1.5	9.026	8.376	58.0	8.5 mm	77%
M10 x 1.25	fine	1.25	9.188	8.647	61.2	8.75 mm	77%
M10 x 1	fine	1	9.350	8.917	64.5	9 mm	77%
M12 x 1.75	coarse	1.75	10.863	10.106	84.3	10.25 mm	77%
M12 x 1.5	fine	1.5	11.026	10.376	88.1	10.5 mm	77%
M12 x 1.25	fine	1.25	11.188	10.647	92.1	10.75 mm	77%
M14 x 2	coarse	2	12.701	11.835	115.4	12 mm	77%
M14 x 1.5	fine	1.5	13.026	12.376	124.5	12.5 mm	77%
M16 x 2	coarse	2	14.701	13.835	156.7	14 mm	77%
M16 x 1.5	fine	1.5	15.026	14.376	167.2	14.5 mm	77%
M18 x 2.5	coarse	2.5	16.376	15.294	192.5	15.5 mm	77%
M18 x 1.5	fine	1.5	17.026	16.376	216.2	16.5 mm	77%
M20 x 2.5	coarse	2.5	18.376	17.294	244.8	17.5 mm	77%
M20 x 1.5	fine	1.5	19.026	18.376	271.5	18.5 mm	77%
M22 x 2.5	coarse	2.5	20.376	19.294	303.4	19.5 mm	77%
M22 x 1.5	fine	1.5	21.026	20.376	333.1	20.5 mm	77%
M24 x 3	coarse	3	22.051	20.752	352.5	21 mm	77%
M24 x 2	fine	2	22.701	21.835	384.4	22 mm	77%
M27 x 3	coarse	3	25.051	23.752	459.4	24 mm	77%
M27 x 2	fine	2	25.701	24.835	495.7	25 mm	77%
M30 x 3.5	coarse	3.5	27.727	26.211	560.6	26.5 mm	77%
M30 x 2	fine	2	28.701	27.835	621.2	28 mm	77%
M36 x 4	coarse	4	33.402	31.670	816.7	32 mm	77%
M36 x 3	fine	3	34.051	32.752	864.9	33 mm	77%

Basic dimensions from the ISO 68-1 profile: pitch dia d2 = d − 0.649519 P; minor dia (internal) D1 = d − 1.082532 P; stress area As = π/4 (d − 0.938194 P)² (ISO 898-1). Tap drill = d − P; thread % = (d − drill) / (1.299 P).

The metric tap drill rule: diameter minus pitch

For metric threads the tap drill is simply the nominal diameter minus the pitch. For M6 x 1 that is 6 − 1 = 5 mm; for M8 x 1.25 it is 6.75 mm, which is usually drilled 6.8 mm; for M12 x 1.75 it is 10.25 mm, drilled 10.2 mm. The rule gives about 77% of full thread depth for every size, because both the pitch and the thread depth scale together. That is slightly more than the 75% usually aimed for with inch threads, and it is the standard choice in steel and aluminium. In stainless steel or with small taps (M3 and below) many machinists drill 0.1 mm larger to make tapping easier.

Worked example: M8 coarse and fine

For M8 x 1.25: pitch diameter = 8 − 0.649519 x 1.25 = 7.188 mm; minor diameter of the nut thread = 8 − 1.082532 x 1.25 = 6.647 mm; stress area = π/4 x (8 − 0.938194 x 1.25)² = 36.6 mm². Tap drill 8 − 1.25 = 6.75 mm. For M8 x 1 the stress area is 39.2 mm² (7% more) and the tap drill is 7 mm. If you have only an inch drill set, the nearest to 6.8 mm is 17/64″ (0.2656 in).

Stress area matters because a bolt fails across its threaded section, not its shank. The stress area of an M12 coarse bolt, 84.3 mm², is the figure a bolt strength class multiplies to give a load rating; for any structural or safety-critical joint, take the rating from the fastener manufacturer or an engineer, not from a chart.

Common mistakes

Assuming every M-size has one pitch. M10, M12 and larger come in several fine pitches; an M10 x 1.25 nut will not fit an M10 x 1.5 bolt. Measure with a metric pitch gauge, which reads the pitch directly in millimetres.
Mixing up metric and inch near-misses: M6 x 1 and 1/4-20 look alike (6 mm against 6.35 mm), as do M5 x 0.8 and #10-24, and M8 x 1.25 and 5/16-18. They may start but will strip.
Drilling the tap hole with a worn or undersized drill and then forcing the tap. If the tap binds, back it out half a turn every turn to break the chip, and use cutting fluid in steel.

Frequently asked questions

What is the pitch of an M6 thread?

1.0 mm for the standard coarse thread. Fine M6 threads (M6 x 0.75) exist but are rare outside specialist uses.

What size drill for an M8 tap?

6.8 mm for M8 x 1.25 coarse (8 − 1.25 = 6.75 mm), and 7.0 mm for M8 x 1 fine.

How do I calculate a metric tap drill size?

Subtract the pitch from the nominal diameter: tap drill = d − P. M10 x 1.5 needs 8.5 mm, M5 x 0.8 needs 4.2 mm, M4 x 0.7 needs 3.3 mm.

What is the difference between coarse and fine metric threads?

Fine threads have a smaller pitch, so more threads per millimetre, a slightly larger stress area and better resistance to loosening. Coarse threads are the default and are better in soft materials.

Sources and method

Every dimension on this page is computed from the formulas below, not copied from another chart, so you can check any row by hand. Values are basic (nominal) dimensions; real parts are made to tolerance classes (2A/2B for inch, 6g/6H for metric) and are slightly smaller (bolts) or larger (nuts and tapped holes).

ASME B1.1, Unified Inch Screw Threads (UN and UNR Thread Form): basic profile, pitch-diameter and minor-diameter relationships, and the tensile stress area formula. The same relationships are published in the US federal standard FED-STD-H28/2B, Screw-Thread Standards for Federal Services, Section 2 (a US Government work).
ISO 68-1, ISO general purpose screw threads, basic profile; ISO 261, general plan of diameters and pitches; ISO 898-1, stress area of metric bolts.
ASME B94.11M, Twist Drills: number, letter and fractional drill diameters (the drill list used by our calculators).
ISO 273, Fasteners, clearance holes for bolts and screws (fine, medium, coarse series); inch close / normal / loose fits as published in the ASME B18.2.8 clearance classes and reproduced in fastener suppliers’ charts.
Percentage-of-thread formula for tap drills: Machinery’s Handbook (Industrial Press), as used by our tap drill size calculator.

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Last reviewed: 24 October 2026. How we build and check our data: methodology and corrections. Spotted an error? Please let us know.