---
type: "thread"
name: "M1.8×0.35"
designation: "M1.8×0.35"
series: "metric-coarse"
series_name: "ISO Metric Coarse"
system: "metric"
size_label: "M1.8"
pitch_in: 0.01378
pitch_mm: 0.35
basic_major_dia_in: 0.07087
basic_major_dia_mm: 1.8
basic_pitch_dia_in: 0.06193
basic_pitch_dia_mm: 1.573
basic_minor_dia_in: 0.05594
basic_minor_dia_mm: 1.421
tap_drill: "1.45 mm"
tap_drill_dia_in: 0.05709
tap_drill_dia_mm: 1.45
tap_drill_thread_pct: 77
clearance_normal_drill: "2.1 mm"
tensile_stress_area_sqin: 0.002637
tensile_stress_area_sqmm: 1.701
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-coarse/m1.8x0.35
---

# M1.8×0.35 Thread — Dimensions, Tap Drill & Clearance

The tap drill for M1.8×0.35 is 1.45 mm — 0.0571 in (1.450 mm) — which leaves 77.0% thread engagement with a cut tap. Basic pitch diameter is 0.0619 in (1.573 mm) and basic minor diameter is 0.0559 in (1.421 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 Coarse
- **Designation**: M1.8×0.35
- **Pitch**: 0.350 mm
- **Tap drill**: 1.45 mm
- **Standard**: ISO 68-1, ISO 261, ISO 262, ISO 965-1, ISO 898-1

## Basic Thread Dimensions for M1.8×0.35

| Property | Inch | Millimetre |
| --- | --- | --- |
| Basic major diameter | 0.0709 | 1.800 |
| Pitch | 0.0138 | 0.350 |
| Basic pitch diameter | 0.0619 | 1.573 |
| Basic minor diameter | 0.0559 | 1.421 |
| External thread root diameter | 0.0540 | 1.371 |
| Sharp V thread height (H) | 0.0119 | 0.303 |

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

## Tap Drill Sizes for M1.8×0.35

Cut taps, from 50% to 85% thread engagement. The shop default is 75% — a 1.45 mm drill.

| Thread % | Target hole Ø (in) | Target hole Ø (mm) | Drill | Drill Ø (in) | Drill Ø (mm) | Actual thread % |
| --- | --- | --- | --- | --- | --- | --- |
| 50% | 0.0619 | 1.573 | 1.55 mm | 0.0610 | 1.550 | 55.0 |
| 60% | 0.0601 | 1.527 | 1.55 mm | 0.0610 | 1.550 | 55.0 |
| 65% | 0.0592 | 1.504 | 1.5 mm | 0.0591 | 1.500 | 66.0 |
| 70% | 0.0583 | 1.482 | 1.5 mm | 0.0591 | 1.500 | 66.0 |
| 75% (default) | 0.0574 | 1.459 | 1.45 mm | 0.0571 | 1.450 | 77.0 |
| 80% | 0.0565 | 1.436 | 1.45 mm | 0.0571 | 1.450 | 77.0 |
| 85% | 0.0557 | 1.414 | 1.4 mm | 0.0551 | 1.400 | 88.0 |

_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 M1.8×0.35

The through-hole a M1.8×0.35 fastener passes freely, not the tapped hole.

| Fit | Drill | Hole Ø (in) | Hole Ø (mm) | Use |
| --- | --- | --- | --- | --- |
| Close | 2 mm | 0.0787 | 2.000 | Located joints, dowelled assemblies |
| Normal | 2.1 mm | 0.0827 | 2.100 | General assembly — the default |
| Loose | 2.2 mm | 0.0866 | 2.200 | Slotted or adjustable joints, weldments |

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

## Tensile Stress Area of M1.8×0.35

| Property | in² | mm² |
| --- | --- | --- |
| Tensile stress area | 0.00264 | 1.70 |

The effective cross-section used to size a M1.8×0.35 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 M1.8×0.35

A M1.8 fastener is not always M1.8×0.35. These are the other standard pitches cut on the same nominal size.

| Thread | Series | Pitch | Tap drill |
| --- | --- | --- | --- |
| [M1.8×0.2](https://shopmath.org/threads/metric-fine/m1.8x0.2.md) | ISO Metric Fine | 0.200 mm | 1.6 mm |

## Sources and Method for M1.8×0.35

### 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 M1.8×0.35

### What is the tap drill size for M1.8×0.35?

The tap drill for M1.8×0.35 is 1.45 mm — 0.0571 in (1.450 mm). That leaves 77.0% thread engagement with a cut tap.

### What is the pitch diameter of M1.8×0.35?

The basic pitch diameter of M1.8×0.35 is 0.0619 in (1.573 mm).

### What is the minor diameter of M1.8×0.35?

The basic minor diameter of M1.8×0.35 is 0.0559 in (1.421 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 M1.8×0.35?

M1.8×0.35 has a pitch of 0.350 mm, the distance from one thread crest to the next.

### What size clearance hole does a M1.8×0.35 fastener need?

close fit 2 mm (0.0787 in (2.000 mm)), normal fit 2.1 mm (0.0827 in (2.100 mm)), loose fit 2.2 mm (0.0866 in (2.200 mm)). The normal fit is the general-assembly default.

### What is the tensile stress area of M1.8×0.35?

The tensile stress area of M1.8×0.35 is 0.00264 in² (1.70 mm²). Multiply it by the fastener material's allowable stress to get a load.

## Related pages

- Smaller in ISO Metric Coarse: [M1.6×0.35](https://shopmath.org/threads/metric-coarse/m1.6x0.35.md) — tap drill 1.25 mm
- Larger in ISO Metric Coarse: [M2×0.4](https://shopmath.org/threads/metric-coarse/m2x0.4.md) — tap drill 1.6 mm
- All ISO Metric Coarse sizes: [ISO Metric Coarse thread chart](https://shopmath.org/threads/metric-coarse.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-coarse/m1.8x0.35) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*