Thread Size Chart

Name: Thread Size Chart
Creator: Manufacturing Processes

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.

Tables: 2
Rows: 42
Units: in, mm
References: 4
Revised: 2026-08-11

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

24 rows

Size	Major diain	Major diamm	UNC TPI	UNC pitchin	UNC pitchmm	UNF TPI	UNF pitchin	UNF pitchmm
#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
No rows match that filter.

24 rows × 9 columnsUnits: in, mm

Basis and references

Read before use

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.

References

Every value on this page was set against at least two of these sources and recomputed rather than transcribed. Where they disagree, the disagreement is recorded in the notes below.

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

18 rows

Thread	Major diamm	Coarse pitchmm	Fine pitch(es)mm	Coarse designation	Minor dia D1, coarsemm
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
No rows match that filter.

18 rows × 6 columnsUnits: mm

Revision and twin

2026-08-11

Last reviewed 2026-08-11. This page carries 42 rows across 2 tables, all of them in the HTML — nothing is paginated, gated or fetched.

Plain-Markdown twin: /charts/thread-size-chart.md

Notes to the tables

4 notes

Where this data disagrees with itself, with other published charts, or with what the number looks like it means.

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.

Questions

6 questions

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.

How to cite this page

Manufacturing Processes. “Thread Size Chart.” manufacturingprocesses.org, last reviewed 2026-08-11. https://manufacturingprocesses.org/charts/thread-size-chart

If you reproduce a table, cite the standard it derives from as well — the references are the primary sources, this page is a cross-checked transcription of them.