---
type: "thread"
name: "M2×0.25"
designation: "M2×0.25"
series: "metric-fine"
series_name: "ISO Metric Fine"
system: "metric"
size_label: "M2"
pitch_in: 0.009843
pitch_mm: 0.25
basic_major_dia_in: 0.07874
basic_major_dia_mm: 2
basic_pitch_dia_in: 0.07236
basic_pitch_dia_mm: 1.838
basic_minor_dia_in: 0.06807
basic_minor_dia_mm: 1.729
tap_drill: "1.75 mm"
tap_drill_dia_in: 0.0689
tap_drill_dia_mm: 1.75
tap_drill_thread_pct: 77
clearance_normal_drill: "2.4 mm"
tensile_stress_area_sqin: 0.003794
tensile_stress_area_sqmm: 2.448
internal_class_assumed: "6H"
standard: "ISO 68-1, ISO 261, ISO 262, ISO 965-1, ISO 898-1"
verified: "August 1, 2026"
url: https://shopmath.org/threads/metric-fine/m2x0.25
---

# M2×0.25 Thread — Dimensions, Tap Drill & Clearance

The tap drill for M2×0.25 is 1.75 mm — 0.0689 in (1.750 mm) — which leaves 77.0% thread engagement with a cut tap. Basic pitch diameter is 0.0724 in (1.838 mm) and basic minor diameter is 0.0681 in (1.729 mm). Tapped-hole figures on this page assume a class 6H thread; drill sizes for 50–85% engagement are in the tap drill table below.

- **Series**: ISO Metric Fine
- **Designation**: M2×0.25
- **Pitch**: 0.250 mm
- **Tap drill**: 1.75 mm
- **Standard**: ISO 68-1, ISO 261, ISO 262, ISO 965-1, ISO 898-1

## Basic Thread Dimensions for M2×0.25

| Property | Inch | Millimetre |
| --- | --- | --- |
| Basic major diameter | 0.0787 | 2.000 |
| Pitch | 0.0098 | 0.250 |
| Basic pitch diameter | 0.0724 | 1.838 |
| Basic minor diameter | 0.0681 | 1.729 |
| External thread root diameter | 0.0667 | 1.693 |
| Sharp V thread height (H) | 0.0085 | 0.217 |

_Basic dimensions are the theoretical values before any tolerance class is applied._

## Tap Drill Sizes for M2×0.25

Cut taps, from 50% to 85% thread engagement. The shop default is 75% — a 1.75 mm drill.

| Thread % | Target hole Ø (in) | Target hole Ø (mm) | Drill | Drill Ø (in) | Drill Ø (mm) | Actual thread % |
| --- | --- | --- | --- | --- | --- | --- |
| 50% | 0.0724 | 1.838 | 1.85 mm | 0.0728 | 1.850 | 46.2 |
| 60% | 0.0711 | 1.805 | 1.8 mm | 0.0709 | 1.800 | 61.6 |
| 65% | 0.0704 | 1.789 | 1.8 mm | 0.0709 | 1.800 | 61.6 |
| 70% | 0.0698 | 1.773 | 1.75 mm | 0.0689 | 1.750 | 77.0 |
| 75% (default) | 0.0691 | 1.756 | 1.75 mm | 0.0689 | 1.750 | 77.0 |
| 80% | 0.0685 | 1.740 | 1.75 mm | 0.0689 | 1.750 | 77.0 |
| 85% | 0.0679 | 1.724 | 1.7 mm | 0.0669 | 1.700 | 92.4 |

_Target hole Ø is the theoretical hole for the stated engagement. The drill column is the nearest size in the standard number/letter/fractional/metric index, and actual thread % is what that real drill produces._

## Clearance Hole Sizes for M2×0.25

The through-hole a M2×0.25 fastener passes freely, not the tapped hole.

| Fit | Drill | Hole Ø (in) | Hole Ø (mm) | Use |
| --- | --- | --- | --- | --- |
| Close | 2.2 mm | 0.0866 | 2.200 | Located joints, dowelled assemblies |
| Normal | 2.4 mm | 0.0945 | 2.400 | General assembly — the default |
| Loose | 2.6 mm | 0.1024 | 2.600 | Slotted or adjustable joints, weldments |

_Clearance holes per ISO 273 (metric) and ASME B18.2.8 (inch)._

## Tensile Stress Area of M2×0.25

| Property | in² | mm² |
| --- | --- | --- |
| Tensile stress area | 0.00379 | 2.45 |

The effective cross-section used to size a M2×0.25 fastener against a load. Multiply it by the material's allowable stress — the area itself carries no strength assumption.

## Other Thread Pitches in the Same Size as M2×0.25

A M2 fastener is not always M2×0.25. These are the other standard pitches cut on the same nominal size.

| Thread | Series | Pitch | Tap drill |
| --- | --- | --- | --- |
| [M2×0.4](https://shopmath.org/threads/metric-coarse/m2x0.4.md) | ISO Metric Coarse | 0.400 mm | 1.6 mm |

## Sources and Method for M2×0.25

### Basic dimensions

- **Source**: ISO 68-1 basic profile and ISO 898-1 tensile stress area; verified in docs/research/data-sourcing.md §3.2; diameter/pitch pairs: ISO 261 / ISO 262 diameter-pitch pairs via Wikipedia (CC BY-SA 4.0); cross-checked against threadlib metric_thread.csv (BSD-3) and FreeCAD CAM metric-internal-6H.csv (LGPL-2.1+); clearance holes: ISO 273 (metric) and ASME B18.2.8 (inch) via FreeCAD FeatureHole.cpp (LGPL-2.1+), cross-checked against bd_warehouse clearance_hole_sizes.csv (Apache-2.0)
- **Method**: computed+compiled
- **Verified against**: threadlib metric_thread.csv (BSD-3-Clause) and FreeCAD CAM metric-internal-6H.csv (LGPL-2.1+), agreeing cell-for-cell — 215 checks passed at 0.001 mm

### Tap drill sizes

- **Source**: Machinery's Handbook %-thread formula (geometry-derived); nearest-standard-drill-to-75% rule verified at 36/39 published chart rows in docs/research/data-sourcing.md §3.4
- **Method**: computed
- **Verified against**: D-P rule verified as exactly the 77.0% thread case

### Formulas

**Tap drill hole diameter, metric threads**

```text
hole Ø  =  D − (%thread ÷ 100) × 1.29904 × P

  D = basic major diameter (mm)
  P = pitch (mm)
```

_1.29904 = 2 × 0.64952, twice the engaged thread height per side on the 60° ISO profile._

**Actual thread engagement of the chosen drill**

```text
%thread  =  (D − drill Ø) ÷ (1.29904 × P) × 100
```

_The drill column rounds to a real drill; this is the engagement that drill actually leaves._

**Tensile stress area, ISO metric threads**

```text
As  =  (π ÷ 4) × ((d₂ + d₃) ÷ 2)²

  d₂ = basic pitch diameter
  d₃ = external thread root diameter
```

_ISO 898-1 form, evaluated on unrounded intermediates._

### Assumptions

- The headline tap drill assumes 75% thread engagement, the general shop default. Every engagement from 50% to 85% is in the tap drill table — change the assumption and the number moves.
- Tap drill figures are for cut taps. Drill diameters are nominal; a worn or run-out drill cuts oversize and reduces engagement further.
- Tapped-hole figures assume a class 6H internal thread, the general-purpose fit.
- Dataset scope: EXCLUDED: ISO 965-1 tolerance-grade formulas (not located — data-sourcing.md open item 2), 6g external limits (single-sourced), form tap drills, M68-M100 (verified demand cliff at M64).

**Data last verified**: August 1, 2026

## Common Questions About M2×0.25

### What is the tap drill size for M2×0.25?

The tap drill for M2×0.25 is 1.75 mm — 0.0689 in (1.750 mm). That leaves 77.0% thread engagement with a cut tap.

### What is the pitch diameter of M2×0.25?

The basic pitch diameter of M2×0.25 is 0.0724 in (1.838 mm).

### What is the minor diameter of M2×0.25?

The basic minor diameter of M2×0.25 is 0.0681 in (1.729 mm). That is the theoretical root of the internal thread, not the drilled hole size — see the tap drill table for the hole to drill.

### What is the thread pitch of M2×0.25?

M2×0.25 has a pitch of 0.250 mm, the distance from one thread crest to the next.

### What size clearance hole does a M2×0.25 fastener need?

close fit 2.2 mm (0.0866 in (2.200 mm)), normal fit 2.4 mm (0.0945 in (2.400 mm)), loose fit 2.6 mm (0.1024 in (2.600 mm)). The normal fit is the general-assembly default.

### What is the tensile stress area of M2×0.25?

The tensile stress area of M2×0.25 is 0.00379 in² (2.45 mm²). Multiply it by the fastener material's allowable stress to get a load.

## Related pages

- Smaller in ISO Metric Fine: [M1.8×0.2](https://shopmath.org/threads/metric-fine/m1.8x0.2.md) — tap drill 1.6 mm
- Larger in ISO Metric Fine: [M2.5×0.35](https://shopmath.org/threads/metric-fine/m2.5x0.35.md) — tap drill 2.15 mm
- All ISO Metric Fine sizes: [ISO Metric Fine thread chart](https://shopmath.org/threads/metric-fine.md)
- Every thread series: [Screw thread reference](https://shopmath.org/threads.md)
- Cross-series chart: [Tap drill chart](https://shopmath.org/charts/tap-drill.md)

---

*Source: [ShopMath](https://shopmath.org/threads/metric-fine/m2x0.25) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*