Metric Thread Table (Coarse)

ISO metric coarse threads M1 to M48 with pitch, tap drill, diameters and tensile stress area.

Metric threads (ISO 261) are named with an M and the nominal outside (major) diameter in millimeters: M10 is a 10 mm thread. When only the diameter is written, the coarse pitch is meant. This table gives that coarse pitch for every common size from M1 to M48, with the tap drill, the pitch and minor diameters and the tensile stress area that strength calculations use.

Use it at the bench to pick a drill, on the drawing board to size a bolt, and in a calculation to find the load a thread can carry. Click a column heading to sort, or type in the filter box to find a size.

The table

22 rows

Thread	Major diameter (mm)	Coarse pitch (mm)	Tap drill, about 75 percent thread (mm)	Pitch diameter (mm)	Minor diameter, external (mm)	Tensile stress area (mm2)
M1	1	0.35	0.65	0.773	0.571	0.35
M2	2	0.45	1.55	1.708	1.448	1.96
M3	3	0.6	2.4	2.61	2.264	4.66
M4	4	0.7	3.3	3.545	3.141	8.78
M5	5	0.8	4.2	4.48	4.019	14.18
M6	6	1	5	5.35	4.773	20.12
M8	8	1.25	6.75	7.188	6.466	36.61
M10	10	1.5	8.5	9.026	8.16	57.99
M12	12	1.75	10.25	10.863	9.853	84.27
M14	14	2	12	12.701	11.546	115.44
M16	16	2	14	14.701	13.546	156.67
M18	18	2.5	15.5	16.376	14.933	192.47
M20	20	2.5	17.5	18.376	16.933	244.79
M22	22	2.5	19.5	20.376	18.933	303.4
M24	24	3	21	22.051	20.319	352.5
M27	27	3	24	25.051	23.319	459.41
M30	30	3.5	26.5	27.727	25.706	560.59
M33	33	3.5	29.5	30.727	28.706	693.55
M36	36	4	32	33.402	31.093	816.72
M39	39	4	35	36.402	34.093	975.75
M42	42	4.5	37.5	39.077	36.479	1120.91
M48	48	5	43	44.752	41.866	1473.15

Source and notes: ISO 261 and ISO 724 (coarse series); d2 = d - 0.64952 P, d3 = d - 1.22687 P, At = pi/4 (d - 0.9382 P)2 (ISO 898-1). Tap drill is d - P, rounded to a stock size in practice.

How to use this table

Find the thread in the first column (for example M8).
Read the coarse pitch: the distance between neighboring thread crests, in millimeters.
For a tapped hole, drill with the tap drill size (about 75 percent thread engagement). Use the nearest stock drill if the exact size is not made.
For strength, multiply the tensile stress area by a stress: the proof stress gives the load a bolt carries without permanent stretch.

Worked example: an M10 class 8.8 bolt

From the table: pitch 1.50 mm, tap drill 8.5 mm, minor diameter 8.160 mm, tensile stress area 58.0 mm².
ISO 898-1 gives class 8.8 a proof stress of 580 MPa and a minimum tensile strength of 800 MPa.
Proof load = 580 MPa × 58.0 mm² = 33.6 kN.
Minimum breaking load = 800 MPa × 58.0 mm² = 46.4 kN.

Notes and cautions

The tap drill column uses d − P, which leaves about 75 percent thread. Softer, stringy materials may prefer a slightly larger drill; hard materials a slightly smaller one.
Common “medium” clearance holes for bolts (ISO 273) are M6: 6.6 mm, M8: 9 mm, M10: 11 mm and M12: 13.5 mm.
The tensile stress area is larger than the area of the minor diameter. It is the area of a notional round bar that fails at the same load as the thread.

FAQ

What does M10 mean?

A metric thread with a nominal outside diameter of 10 mm. Written alone it means the coarse pitch, which for M10 is 1.5 mm. A fine-pitch version is written with the pitch, for example M10 x 1.25.

What is the difference between coarse and fine threads?

Fine threads have a smaller pitch, so more threads per length. They have a larger stress area for the same diameter, resist loosening better and allow finer adjustment, but they strip more easily in soft materials and cross-thread more easily. Coarse is the default choice.

Why is the tensile stress area bigger than the minor-diameter area?

A thread fails through a section somewhere between the pitch diameter and the minor diameter. The standard stress area is defined from the mean of the two, so it is a fair measure of the strength of the whole bolt.

Sources

ISO 261, ISO 262 and ISO 724 (ISO general-purpose metric screw threads).
ISO 898-1, Mechanical properties of fasteners made of carbon steel and alloy steel.
ISO 261 and ISO 724 (coarse series); d2 = d – 0.64952 P, d3 = d – 1.22687 P, At = pi/4 (d – 0.9382 P)2 (ISO 898-1). Tap drill is d – P, rounded to a stock size in practice.