What is the tap drill size for M10x1.25?

8.8 mm at about 75% thread engagement. It is found by taking major diameter − pitch (10 − 1.25 = 8.750 mm) and selecting the nearest standard metric drill.

What is the pitch diameter of M10x1.25?

9.188 mm. This is the diameter at which thread and groove widths are equal and is the dimension that controls assembly — a thread can meet its major and minor limits and still not fit if the pitch diameter is wrong.

What is the tensile stress area of M10x1.25?

61.20 mm², per ISO 898-1. It is calculated from the pitch diameter and the minor diameter rather than the nominal 10 mm, because the nominal diameter overstates the load-bearing section by roughly a third.

Are the dimensions on this page toleranced?

No. These are basic dimensions — the theoretical profile before any allowance is applied. For a threaded assembly, specify the tolerance class (6g/6H is the normal commercial fit) and use the limit dimensions from ISO 965.

M10x1.25 Thread Dimensions

Dimensions for the M10x1.25 Metric Fine Threads (ISO 261) thread — pitch, pitch diameter, external and internal minor diameters, tap drill and tensile stress area.

Data verified 2026-09-29 · based on ISO 261:1998

Quick Answer

M10x1.25 has a pitch of 1.25 mm, a basic pitch diameter of 9.188 mm and a tap drill size of 8.8 mm at about 75% thread engagement.

Thread Calculator

Major diameter (inch)

Threads per inch

Basic Dimensions

Dimension	Symbol	Inch	Millimetre
Major diameter (external) #	`d`	10	10
Pitch diameter (basic) #	`d2`	9.188	9.188
Minor diameter, external thread #	`d1`	8.466	8.466
Minor diameter, internal thread #	`D1`	8.647	8.647
Pitch #	`P`	1.250	1.250
Thread height, external #	`h`	0.767	0.767
Thread height, internal #	`hn`	0.677	0.677
Crest flat #	`f`	0.156	0.156
Tensile stress area #	`As`	61.198	61.20²

Tap Drill Size

For a M10x1.25 thread at approximately 75% thread engagement, the tap drill is 8.8 mm (8.8 in / 8.8 mm).

Pilot diameter is computed as major diameter − pitch = 10 − 1.25 = 8.750 in, then rounded to the nearest standard drill in the number, letter or fractional series. Increasing engagement above 75% raises tapping torque sharply and risks tap breakage; decreasing it weakens the thread. See the tap drill size chart for the full series.

How to Read the Designation

M10x1.25 gives the nominal major diameter and the pitch directly in millimetres: 10 mm diameter and 1.25 mm pitch. This is the Metric Fine Threads (ISO 261) series.

Writing the pitch explicitly distinguishes this size from the other pitches available at the same diameter. An unqualified M10 would mean the coarse pitch for that diameter.

Tolerance Class

The dimensions on this page are the basic profile — no tolerance class allowance is applied. Production metric threads are specified by a tolerance class such as 6g (external) or 6H (internal), which is the normal commercial fit and the default when none is stated.

Coarser classes (8g, 7H) ease assembly and tolerate plating; finer classes (4h, 5H) are used where a precise fit is needed. The basic dimensions below are the reference from which those limits are derived.

← M8x1 All METRIC-FINE sizes M10x1 →

Frequently Asked Questions

What is the tap drill size for M10x1.25?: 8.8 mm at about 75% thread engagement. It is found by taking major diameter − pitch (10 − 1.25 = 8.750 mm) and selecting the nearest standard metric drill.
What is the pitch diameter of M10x1.25?: 9.188 mm. This is the diameter at which thread and groove widths are equal and is the dimension that controls assembly — a thread can meet its major and minor limits and still not fit if the pitch diameter is wrong.
What is the tensile stress area of M10x1.25?: 61.20 mm², per ISO 898-1. It is calculated from the pitch diameter and the minor diameter rather than the nominal 10 mm, because the nominal diameter overstates the load-bearing section by roughly a third.
Are the dimensions on this page toleranced?: No. These are basic dimensions — the theoretical profile before any allowance is applied. For a threaded assembly, specify the tolerance class (6g/6H is the normal commercial fit) and use the limit dimensions from ISO 965.

Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

#	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	standard	n/a — industry standard series — source
[3]	ISO 261 — ISO general purpose metric screw threads — General plan	standard	ISO 261:1998 — source
[4]	ISO 68-1 — ISO general purpose screw threads — Basic profile	standard	ISO 68-1:2023 — source
[5]	ISO 898-1 — Mechanical properties of fasteners, Part 1: Bolts, screws and studs	standard	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 nominal diameter and pitch of this size
ISO 68-1 — Basic profile	ISO 68-1:2023	the thread form geometry from which every dimension here is computed
ISO 898-1 — Mechanical properties of fasteners	ISO 898-1:2013	the tensile stress area formula

Cross-checked against:

Tensile stress area verified at build time against ISO 898-1 reference values for the coarse series
Basic pitch and minor diameters verified against ISO 724 tabulated values

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

Value	How it is derived
Pitch diameter, minor diameters, thread heights, tensile stress area	Computed from the ISO 68-1 basic profile and the ISO 898-1 stress-area formula — see the Value Sources table above.

Basic dimensions only, with no tolerance class allowance. Specify a class (6g/6H is standard) for a threaded assembly and use ISO 965 limit dimensions.

Accuracy and use. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. 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.

Cite This Page

Every value on this page is traceable to the sources listed above. If you use the data in a document, paper or report, cite it as:

Plain text

Engineering Reference. "M10x1.25 Thread Dimensions." https://refmanual.com/threads/metric-fine/m10x1-25/ (accessed 2026-09-29). Data from ISO 261 — General plan for metric screw threads, ISO 261:1998.

BibTeX

@misc{m10x1-25,
  title        = {M10x1.25 Thread Dimensions},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/threads/metric-fine/m10x1-25/}},
  note         = {Accessed: 2026-09-29},
  source       = {ISO 261 — General plan for metric screw threads, ISO 261:1998}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - M10x1.25 Thread Dimensions
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/threads/metric-fine/m10x1-25/
PY  - 2026
DA  - 2026-09-29
N1  - Source: ISO 261 — General plan for metric screw threads, ISO 261:1998
ER  -

Each row in the tables above also has a permanent link — hover a row and use the # link to cite a single value rather than the whole page.