What is the tap drill size for an M10 thread?

For M10x1.5 coarse, the tap drill is 8.5 mm. For M10x1.25 fine it is 8.8 mm, and for M10x1 it is 9.0 mm. The pilot diameter is the nominal diameter minus the pitch, rounded to the nearest standard metric drill, taking the larger on a tie. This is a starting estimate, not a specified thread percentage.

What is the difference between M10 and M10x1.5?

They are the same thread. Unqualified M10 means the coarse pitch for that diameter, which is 1.5 mm, so M10 and M10x1.5 are identical. Writing the pitch explicitly is done to distinguish it from the fine pitches available at the same diameter — M10x1.25 and M10x1.

Are metric and inch threads interchangeable?

No, even at matching nominal diameters. Metric threads use a 60° included angle with the diameter and pitch specified in millimetres; unified inch threads also use 60° but with inch dimensions and a different root form. A 10 mm and a 3/8 in thread differ in both diameter and pitch, and will not assemble properly.

What is the tensile stress area of an M10 bolt?

58.0 mm² for M10x1.5 coarse, per ISO 898-1. It is calculated as π/4 × (d − 0.9382P)², which uses a diameter between the pitch diameter and the minor diameter rather than the nominal diameter — using the nominal 10 mm would overstate the strength by about 35%.

Metric Coarse Threads (ISO 261)

Every standard metric coarse size with pitch, pitch diameter, minor diameters, tap drill and tensile stress area — computed from the ISO 68-1 basic profile.

Page last changed 2026-10-19 · based on ISO 261:1998

Quick Answer

Metric Coarse Threads (ISO 261) covers 20 sizes in this table. The designation states the nominal diameter and the pitch in millimetres — M10x1.5 is a 10 mm nominal diameter at a 1.5 mm pitch. Dimensions below are basic and carry no tolerance class allowance.

Find a size

Metric Coarse Threads (ISO 261) Chart

Size^[3]	Pitch mm^[3]	Major dia mm^[1]	Pitch dia mm^[1]	Ext. minor mm^[1]	Int. minor mm^[1]	Tap drill mm^[2]	Tensile area mm²^[5]
M1.6x0.35 #	0.35	1.6	1.373	1.171	1.221	1.3 mm	1.27
M2x0.4 #	0.4	2	1.740	1.509	1.567	1.6 mm	2.07
M2.5x0.45 #	0.45	2.5	2.208	1.948	2.013	2.1 mm	3.39
M3x0.5 #	0.5	3	2.675	2.387	2.459	2.5 mm	5.03
M4x0.7 #	0.7	4	3.545	3.141	3.242	3.3 mm	8.78
M5x0.8 #	0.8	5	4.480	4.019	4.134	4.2 mm	14.18
M6x1 #	1	6	5.350	4.773	4.917	5 mm	20.12
M8x1.25 #	1.25	8	7.188	6.466	6.647	6.8 mm	36.61
M10x1.5 #	1.5	10	9.026	8.160	8.376	8.5 mm	57.99
M12x1.75 #	1.75	12	10.863	9.853	10.106	10.3 mm	84.27
M14x2 #	2	14	12.701	11.546	11.835	12 mm	115.44
M16x2 #	2	16	14.701	13.546	13.835	14 mm	156.67
M20x2.5 #	2.5	20	18.376	16.933	17.294	17.5 mm	244.79
M24x3 #	3	24	22.051	20.319	20.752	21 mm	352.50
M30x3.5 #	3.5	30	27.727	25.706	26.211	26.5 mm	560.59
M36x4 #	4	36	33.402	31.093	31.670	32 mm	816.72
M42x4.5 #	4.5	42	39.077	36.479	37.129	37.5 mm	1120.91
M48x5 #	5	48	44.752	41.866	42.587	43 mm	1473.15
M56x5.5 #	5.5	56	52.428	49.252	50.046	50.5 mm	2030.02
M64x6 #	6	64	60.103	56.639	57.505	58 mm	2675.97

All dimensions are basic — the theoretical profile with no tolerance class allowance. Tap drills are cutting-tap starting sizes; confirm the selected tool’s hole range. Tensile stress area follows ISO 898-1: for M10x1.5 it is 58.0 mm².

How Metric Designations Work

A metric thread designation gives the nominal major diameter and the pitch directly: M10x1.5 is a 10 mm major diameter with a 1.5 mm pitch. Where only the diameter is written — M10 — the coarse pitch for that diameter is implied.

This is different from the inch system, where the pitch appears as "threads per inch" and is written after a hyphen (1/4-20). A metric pitch of 1.5 mm corresponds to 16.9 threads per inch — metric and inch threads are not interchangeable even at the same nominal diameter, because the thread angles and diameters differ.

Coarse vs Fine Pitch

ISO 261 defines a coarse series, one per diameter, and a fine series with several options per diameter. Coarse is the default and is what an unqualified M10 means.

Coarse — deeper thread, more resistant to cross-threading and to damage, and forgiving of plating thickness. The normal choice for general fastening in steel.
Fine — shallower thread, larger minor diameter for the same nominal size, so higher tensile strength and better resistance to vibration loosening. Used on thin-walled parts, in higher-strength materials, and for adjustment.

The cost of fine threads is a thinner wall at the crest of the internal thread — in soft or thin materials coarse is usually the safer choice.

Frequently Asked Questions

What is the tap drill size for an M10 thread?: For M10x1.5 coarse, the tap drill is 8.5 mm. For M10x1.25 fine it is 8.8 mm, and for M10x1 it is 9.0 mm. The pilot diameter is the nominal diameter minus the pitch, rounded to the nearest standard metric drill, taking the larger on a tie. This is a starting estimate, not a specified thread percentage.
What is the difference between M10 and M10x1.5?: They are the same thread. Unqualified M10 means the coarse pitch for that diameter, which is 1.5 mm, so M10 and M10x1.5 are identical. Writing the pitch explicitly is done to distinguish it from the fine pitches available at the same diameter — M10x1.25 and M10x1.
Are metric and inch threads interchangeable?: No, even at matching nominal diameters. Metric threads use a 60° included angle with the diameter and pitch specified in millimetres; unified inch threads also use 60° but with inch dimensions and a different root form. A 10 mm and a 3/8 in thread differ in both diameter and pitch, and will not assemble properly.
What is the tensile stress area of an M10 bolt?: 58.0 mm² for M10x1.5 coarse, per ISO 898-1. It is calculated as π/4 × (d − 0.9382P)², which uses a diameter between the pitch diameter and the minor diameter rather than the nominal diameter — using the nominal 10 mm would overstate the strength by about 35%.

Value Sources

References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.

#	Source	Type	Revision / method
[1]	Basic dimensions computed from the ISO 68-1 basic profile	derived	H = √3/2 × P. Pitch diameter d2 = d − 0.75H. External minor diameter d1 = d − 2(0.61343P). Internal minor diameter D1 = d − 2(0.54127P). Tensile stress area As = π/4 × (d − 0.9382P)² per ISO 898-1.
[2]	Standard metric twist drill series	reference	n/a — industry standard series — source
[3]	ISO 261 — ISO general purpose metric screw threads — General plan	reference	ISO 261:1998 — source
[4]	ISO 68-1 — ISO general purpose screw threads — Basic profile	reference	ISO 68-1:2023 — source
[5]	ISO 898-1 — Mechanical properties of fasteners, Part 1: Bolts, screws and studs	reference	ISO 898-1:2013

Data Sources

Standard	Revision	What it covers on this page
ISO 261 — General plan for metric screw threads	ISO 261:1998	the diameter and pitch series
ISO 68-1 — Basic profile	ISO 68-1:2023	the thread form geometry from which every dimension is computed
ISO 898-1 — Mechanical properties of fasteners	ISO 898-1:2013	the tensile stress area formula

Verification scope

No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.

Derived values — the following values on this page are calculated, not taken directly from the standard:

Value	How it is derived
All dimensions and the tensile stress area	Computed from the ISO 68-1 basic profile and the ISO 898-1 stress-area formula — see the Value Sources table.

Dimensions are basic and carry no tolerance class allowance. For a threaded assembly, specify the tolerance class (for example 6g/6H) and use the limit dimensions from ISO 965.

Accuracy and use. Use the source notes and recorded verification scope above to assess each value. Calculated values follow the stated derivations; compilation values may lack a confirmed original document or product condition. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

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Read the source notes, calculation methods and verification scope above before reusing a value. To cite this page:

Plain text

Engineering Reference. "Metric Coarse Threads (ISO 261)." https://refmanual.com/charts/metric-coarse-thread-sizes/ (accessed 2026-10-19). Data from ISO 261 — General plan for metric screw threads, ISO 261:1998.

BibTeX

@misc{metric-coarse-thread-sizes,
  title        = {Metric Coarse Threads (ISO 261)},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/metric-coarse-thread-sizes/}},
  note         = {Accessed: 2026-10-19},
  source       = {ISO 261 — General plan for metric screw threads, ISO 261:1998}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Metric Coarse Threads (ISO 261)
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/metric-coarse-thread-sizes/
PY  - 2026
DA  - 2026-10-19
N1  - Source: ISO 261 — General plan for metric screw threads, ISO 261:1998
ER  -

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