---
type: chart
title: "Thread Size Chart"
tables: 2
url: https://manufacturingprocesses.org/charts/thread-size-chart
---

# Thread Size Chart

Unified inch threads #0 to 1-1/2 with UNC and UNF pitches, and ISO metric threads M1.6 to M24 with coarse and fine pitches and basic minor diameters.

Both thread systems on this page use the same 60° symmetric V profile; only
the diameter and pitch pairings differ. Unified inch threads (ASME B1.1)
are specified by threads per inch, so pitch is the reciprocal of TPI. ISO
metric threads (ISO 261 general plan, ISO 262 selected sizes) are specified
by pitch in millimeters directly.

The **basic minor diameter** column, D1 = D − 1.0825 × P, is the number that
governs tap drill selection and thread shear area. It is computed here, not
transcribed. Pitch columns on the inch table are likewise computed as 1/TPI
and then converted at exactly 25.4 mm/in.

Numbered inch sizes follow their own rule: major diameter = (screw number ×
0.013) + 0.060 in. That gives #0 = 0.060, #6 = 0.138, #10 = 0.190 in.

## Unified inch threads (UNC / UNF), ASME B1.1

| Size | Major dia (in) | Major dia (mm) | UNC TPI | UNC pitch (in) | UNC pitch (mm) | UNF TPI | UNF pitch (in) | UNF pitch (mm) |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| #0 | 0.06 | 1.524 | — | — | — | 80 | 0.0125 | 0.3175 |
| #1 | 0.073 | 1.8542 | 64 | 0.015625 | 0.3969 | 72 | 0.013889 | 0.3528 |
| #2 | 0.086 | 2.1844 | 56 | 0.017857 | 0.4536 | 64 | 0.015625 | 0.3969 |
| #3 | 0.099 | 2.5146 | 48 | 0.020833 | 0.5292 | 56 | 0.017857 | 0.4536 |
| #4 | 0.112 | 2.8448 | 40 | 0.025 | 0.635 | 48 | 0.020833 | 0.5292 |
| #5 | 0.125 | 3.175 | 40 | 0.025 | 0.635 | 44 | 0.022727 | 0.5773 |
| #6 | 0.138 | 3.5052 | 32 | 0.03125 | 0.7937 | 40 | 0.025 | 0.635 |
| #8 | 0.164 | 4.1656 | 32 | 0.03125 | 0.7937 | 36 | 0.027778 | 0.7056 |
| #10 | 0.19 | 4.826 | 24 | 0.041667 | 1.0583 | 32 | 0.03125 | 0.7937 |
| #12 | 0.216 | 5.4864 | 24 | 0.041667 | 1.0583 | 28 | 0.035714 | 0.9071 |
| 1/4 | 0.25 | 6.35 | 20 | 0.05 | 1.27 | 28 | 0.035714 | 0.9071 |
| 5/16 | 0.3125 | 7.9375 | 18 | 0.055556 | 1.4111 | 24 | 0.041667 | 1.0583 |
| 3/8 | 0.375 | 9.525 | 16 | 0.0625 | 1.5875 | 24 | 0.041667 | 1.0583 |
| 7/16 | 0.4375 | 11.1125 | 14 | 0.071429 | 1.8143 | 20 | 0.05 | 1.27 |
| 1/2 | 0.5 | 12.7 | 13 | 0.076923 | 1.9538 | 20 | 0.05 | 1.27 |
| 9/16 | 0.5625 | 14.2875 | 12 | 0.083333 | 2.1167 | 18 | 0.055556 | 1.4111 |
| 5/8 | 0.625 | 15.875 | 11 | 0.090909 | 2.3091 | 18 | 0.055556 | 1.4111 |
| 3/4 | 0.75 | 19.05 | 10 | 0.1 | 2.54 | 16 | 0.0625 | 1.5875 |
| 7/8 | 0.875 | 22.225 | 9 | 0.111111 | 2.8222 | 14 | 0.071429 | 1.8143 |
| 1 | 1 | 25.4 | 8 | 0.125 | 3.175 | 12 | 0.083333 | 2.1167 |
| 1-1/8 | 1.125 | 28.575 | 7 | 0.142857 | 3.6286 | 12 | 0.083333 | 2.1167 |
| 1-1/4 | 1.25 | 31.75 | 7 | 0.142857 | 3.6286 | 12 | 0.083333 | 2.1167 |
| 1-3/8 | 1.375 | 34.925 | 6 | 0.166667 | 4.2333 | 12 | 0.083333 | 2.1167 |
| 1-1/2 | 1.5 | 38.1 | 6 | 0.166667 | 4.2333 | 12 | 0.083333 | 2.1167 |

## ISO metric threads M1.6 – M24 (ISO 261 / ISO 262)

| Thread | Major dia (mm) | Coarse pitch (mm) | Fine pitch(es) (mm) | Coarse designation | Minor dia D1, coarse (mm) |
| --- | --- | --- | --- | --- | --- |
| M1.6 | 1.6 | 0.35 | 0.2 | M1.6 × 0.35 | 1.221 |
| M2 | 2 | 0.4 | 0.25 | M2 × 0.4 | 1.567 |
| M2.5 | 2.5 | 0.45 | 0.35 | M2.5 × 0.45 | 2.013 |
| M3 | 3 | 0.5 | 0.35 | M3 × 0.5 | 2.459 |
| M3.5 | 3.5 | 0.6 | 0.35 | M3.5 × 0.6 | 2.851 |
| M4 | 4 | 0.7 | 0.5 | M4 × 0.7 | 3.242 |
| M5 | 5 | 0.8 | 0.5 | M5 × 0.8 | 4.134 |
| M6 | 6 | 1 | 0.75 | M6 × 1 | 4.918 |
| M7 | 7 | 1 | 0.75 | M7 × 1 | 5.918 |
| M8 | 8 | 1.25 | 1 / 0.75 | M8 × 1.25 | 6.647 |
| M10 | 10 | 1.5 | 1.25 / 1 | M10 × 1.5 | 8.376 |
| M12 | 12 | 1.75 | 1.5 / 1.25 | M12 × 1.75 | 10.106 |
| M14 | 14 | 2 | 1.5 | M14 × 2 | 11.835 |
| M16 | 16 | 2 | 1.5 | M16 × 2 | 13.835 |
| M18 | 18 | 2.5 | 2 / 1.5 | M18 × 2.5 | 15.294 |
| M20 | 20 | 2.5 | 2 / 1.5 | M20 × 2.5 | 17.294 |
| M22 | 22 | 2.5 | 2 / 1.5 | M22 × 2.5 | 19.294 |
| M24 | 24 | 3 | 2 | M24 × 3 | 20.753 |

## Notes

**1 in UNF is 1-12, but 1-14 is what is actually stocked.** The Unified
standard fine pitch for 1 in is 12 TPI. 1-14 is far more widely available
and is commonly — and incorrectly — called "1 inch UNF". If you specify a
1 in fine thread, state the TPI explicitly.

**Several metric diameters have more than one fine pitch.** M8, M10, M12,
M18, M20 and M22 each list two; the first shown is the more common. M24 has
only one fine pitch, 2.0 mm.

**A widely republished 9/16 row contains typos.** One source lists
"9/16-12 2A 0.5609" against a basic major diameter of 0.5625, and
"9/16-12 3A … 0.511". The basic major diameter for 9/16 is 0.5625 in by
definition (9 ÷ 16); the TPI data is unaffected.

All 24 UNC/UNF diameter–TPI pairings were cross-verified between two
independent sources, and the computed pitches were spot-checked against a
published pitch column at #6-32, 1/4-20 and 1/2-13 with exact agreement.

## FAQ

### What is the coarse pitch of an M6 thread?

1.0 mm. The full designation is M6 × 1, its basic minor diameter is 4.918 mm, and its fine pitch alternative is 0.75 mm.

### What is the difference between UNC and UNF?

Only the number of threads per inch at the same major diameter. 1/4-20 is UNC (coarse) and 1/4-28 is UNF (fine). Fine threads have a larger minor diameter and so a larger tensile stress area, and they resist loosening slightly better; coarse threads tolerate damage and dirt better and assemble faster.

### How do I convert threads per inch to pitch?

Pitch is the reciprocal of TPI. 1/4-20 has a pitch of 1/20 = 0.050000 in, which is 1.2700 mm. 1/2-13 gives 0.076923 in, or 1.9538 mm.

### What is the minor diameter of a thread and why does it matter?

The basic internal minor diameter is D1 = D − 1.0825 × P — the diameter at the root of an internal thread. It sets the thread shear area and it is the number tap drill selection works back from. For M10 × 1.5 it is 8.376 mm.

### How big is a #10 screw?

0.1900 in (4.826 mm) major diameter. Numbered inch sizes follow major diameter = (number × 0.013) + 0.060 in, so #10 = (10 × 0.013) + 0.060 = 0.190 in.

### Is 1 inch UNF 12 or 14 threads per inch?

The standard says 12. 1-14 is much more widely stocked and is often loosely called "1 inch UNF", so a drawing that says 1 in UNF without a TPI is ambiguous. State the TPI.

## Sources

- [Wikipedia — Unified Thread Standard (cited to Machinery's Handbook 29th ed., p. 1816)](https://en.wikipedia.org/wiki/Unified_Thread_Standard)
- [Engineers Edge — ANSI External Screw Threads Size & Tolerances Chart](https://www.engineersedge.com/screw_threads_chart.htm)
- [Wikipedia — ISO metric screw thread (ISO 262 selected sizes)](https://en.wikipedia.org/wiki/ISO_metric_screw_thread)
- [Machining Doctor — Unified Threads (UNC/UNF/UNEF): Dimensions & Formulas](https://www.machiningdoctor.com/charts/unified-inch-threads-charts/)

## Related processes

- [Mechanical Fastening](https://manufacturingprocesses.org/processes/joining/mechanical-fastening.md)
- [Swiss Screw Machining](https://manufacturingprocesses.org/processes/cutting/swiss-screw-machining.md)
- [CNC Turning](https://manufacturingprocesses.org/processes/cutting/cnc-turning.md)

## Related charts

- [Tap Drill Chart](https://manufacturingprocesses.org/charts/tap-drill-chart.md)
- [Drill Size Chart](https://manufacturingprocesses.org/charts/drill-size-chart.md)
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---

*Source: [Manufacturing Processes](https://manufacturingprocesses.org/charts/thread-size-chart)*

*Last updated: August 11, 2026*