---
type: "thread"
name: "M33×2"
designation: "M33×2"
series: "metric-fine"
series_name: "ISO Metric Fine"
system: "metric"
size_label: "M33"
pitch_in: 0.07874
pitch_mm: 2
basic_major_dia_in: 1.29921
basic_major_dia_mm: 33
basic_pitch_dia_in: 1.24807
basic_pitch_dia_mm: 31.701
basic_minor_dia_in: 1.21398
basic_minor_dia_mm: 30.835
tap_drill: "25 mm"
tap_drill_dia_in: 0.98425
tap_drill_dia_mm: 25
tap_drill_thread_pct: 307.9
clearance_normal_drill: "25 mm"
tensile_stress_area_sqin: 1.179241
tensile_stress_area_sqmm: 760.799
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/m33x2
---

# M33×2 Thread — Dimensions, Tap Drill & Clearance

The tap drill for M33×2 is 25 mm — 0.9842 in (25.000 mm) — which leaves 307.9% thread engagement with a cut tap. Basic pitch diameter is 1.2481 in (31.701 mm) and basic minor diameter is 1.2140 in (30.835 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**: M33×2
- **Pitch**: 2.000 mm
- **Tap drill**: 25 mm
- **Standard**: ISO 68-1, ISO 261, ISO 262, ISO 965-1, ISO 898-1

## Basic Thread Dimensions for M33×2

| Property | Inch | Millimetre |
| --- | --- | --- |
| Basic major diameter | 1.2992 | 33.000 |
| Pitch | 0.0787 | 2.000 |
| Basic pitch diameter | 1.2481 | 31.701 |
| Basic minor diameter | 1.2140 | 30.835 |
| External thread root diameter | 1.2026 | 30.546 |
| Sharp V thread height (H) | 0.0682 | 1.732 |

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

## Tap Drill Sizes for M33×2

Cut taps, from 50% to 85% thread engagement. The shop default is 75% — a 25 mm drill.

| Thread % | Target hole Ø (in) | Target hole Ø (mm) | Drill | Drill Ø (in) | Drill Ø (mm) | Actual thread % |
| --- | --- | --- | --- | --- | --- | --- |
| 50% | 1.2481 | 31.701 | 25 mm | 0.9843 | 25.000 | 307.9 |
| 60% | 1.2378 | 31.441 | 25 mm | 0.9843 | 25.000 | 307.9 |
| 65% | 1.2327 | 31.311 | 25 mm | 0.9843 | 25.000 | 307.9 |
| 70% | 1.2276 | 31.181 | 25 mm | 0.9843 | 25.000 | 307.9 |
| 75% (default) | 1.2225 | 31.051 | 25 mm | 0.9843 | 25.000 | 307.9 |
| 80% | 1.2174 | 30.922 | 25 mm | 0.9843 | 25.000 | 307.9 |
| 85% | 1.2123 | 30.792 | 25 mm | 0.9843 | 25.000 | 307.9 |

_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 M33×2

The through-hole a M33×2 fastener passes freely, not the tapped hole.

| Fit | Drill | Hole Ø (in) | Hole Ø (mm) | Use |
| --- | --- | --- | --- | --- |
| Close | 25 mm | 1.3386 | 34.000 | Located joints, dowelled assemblies |
| Normal | 25 mm | 1.4173 | 36.000 | General assembly — the default |
| Loose | 25 mm | 1.4961 | 38.000 | Slotted or adjustable joints, weldments |

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

## Thread Class Limits for M33×2

Manufacturing limits for classes 6H. A gauge reading outside these bands is a reject, not a judgement call.

### Internal thread (nut / tapped hole) limits

| Limit | Class 6H (in) | Class 6H (mm) |
| --- | --- | --- |
| Major Ø min | 1.2992 | 33.000 |
| Pitch Ø max | 1.2569 | 31.925 |
| Pitch Ø min | 1.2481 | 31.701 |
| Pitch Ø tolerance | — | 0.224 |
| Minor Ø max | 1.2287 | 31.210 |
| Minor Ø min | 1.2140 | 30.835 |

## Tensile Stress Area of M33×2

| Property | in² | mm² |
| --- | --- | --- |
| Tensile stress area | 1.17924 | 760.80 |

The effective cross-section used to size a M33×2 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 M33×2

A M33 fastener is not always M33×2. These are the other standard pitches cut on the same nominal size.

| Thread | Series | Pitch | Tap drill |
| --- | --- | --- | --- |
| [M33×3.5](https://shopmath.org/threads/metric-coarse/m33x3.5.md) | ISO Metric Coarse | 3.500 mm | 25 mm |

## Sources and Method for M33×2

### 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

### Class limits

- **Source**: threadlib metric_thread.csv (BSD-3-Clause) and FreeCAD CAM metric-internal-6H.csv (LGPL-2.1+), agreeing cell-for-cell
- **Method**: compiled
- **Verified against**: two independent published datasets agreeing cell-for-cell to 0.001 mm; ISO 965-1 formulas not located, so these are compiled not computed

### 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 M33×2

### What is the tap drill size for M33×2?

The tap drill for M33×2 is 25 mm — 0.9842 in (25.000 mm). That leaves 307.9% thread engagement with a cut tap.

### What is the pitch diameter of M33×2?

The basic pitch diameter of M33×2 is 1.2481 in (31.701 mm). For a class 6H thread it runs 1.2481 in (31.701 mm) to 1.2569 in (31.925 mm).

### What is the minor diameter of M33×2?

The basic minor diameter of M33×2 is 1.2140 in (30.835 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 M33×2?

M33×2 has a pitch of 2.000 mm, the distance from one thread crest to the next.

### What size clearance hole does a M33×2 fastener need?

close fit 25 mm (1.3386 in (34.000 mm)), normal fit 25 mm (1.4173 in (36.000 mm)), loose fit 25 mm (1.4961 in (38.000 mm)). The normal fit is the general-assembly default.

### What is the tensile stress area of M33×2?

The tensile stress area of M33×2 is 1.17924 in² (760.80 mm²). Multiply it by the fastener material's allowable stress to get a load.

## Related pages

- Smaller in ISO Metric Fine: [M30×2](https://shopmath.org/threads/metric-fine/m30x2.md) — tap drill 25 mm
- Larger in ISO Metric Fine: [M36×3](https://shopmath.org/threads/metric-fine/m36x3.md) — tap drill 25 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/m33x2) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*