Plumbing fitting and pipe thread standards
Dimensional specifications for NPT and BSP pipe thread sizes used in plumbing, hydraulic, and gas fittings worldwide. For each nominal pipe size within each standard, gives threads per inch, pitch, major diameter, and minor diameter — the numbers needed to identify an unknown thread or confirm whether two fittings will mate. Combines American (ASME B1.20.1) and British/ISO (ISO 228, ISO 7) standards in one table so the critical differences are visible side by side.
Records97
Sources8
Verified
Review by
Licencefactual compilation of thread dimensions from public reference sources; facts cited with attributed quotes, no standard document reproduced
21 records where two or more sources state different values. Both sides are reproduced on the record page, each with its own source and quote.
The data
| Nominal size | Thread standard | Threads per inch (TPI) | Thread pitch (mm) | Major (outside) diameter (mm) | Minor diameter (mm) | Thread angle (degrees) | Governing standard |
|---|---|---|---|---|---|---|---|
| 1sources differ | BSP | 11 | 2.309 | 33.249 | 30.291 | 55 | ISO 228-1 |
| 1-1/2sources differ | BSP | 11 | 2.309 | 47.803 | 44.845 | 55 | ISO 228-1 |
| 1-1/2 | NPT | 11 1/2 | 2.2087 | 48.2600 | 60 | ASME B1.20.1 | |
| 1 1/2 | BSPT | 11 | 2.309 | 47.80 | 44.85 | 55 | ISO 7-1 |
| 1 1/2 | BSPP | 11 | 2.309 | 47.803 | 44.846 | 55 | ISO 228-1 |
| 1-1/2 Inch BSP | BSP | 11 | 47.80 | ||||
| 1-1/4sources differ | BSP | 11 | 2.309 | 41.910 | 38.952 | 55 | ISO 228-1 |
| 1-1/4 | NPT | 11 1/2 | 2.2087 | 42.1640 | 60 | ASME B1.20.1 | |
| 1 1/4 | BSPT | 11 | 2.309 | 41.91 | 38.95 | 55 | ISO 7-1 |
| 1 1/4 | BSPP | 11 | 2.309 | 41.910 | 38.953 | 55 | ISO 228-1 |
| 1-1/4 Inch BSP | BSP | 11 | 41.91 | ||||
| 1-1/8 | BSP | 11 | 2.309 | 37.897 | 34.939 | 55 | ISO 228-1 |
| 1 1/8 | BSPP | 11 | 2.309 | 37.897 | 34.940 | 55 | ISO 228-1 |
| 1 | BSPP | 11 | 2.309 | 33.249 | 30.292 | 55 | ISO 228-1 |
| 1/16 | BSP | 28 | 0.907 | 7.723 | 6.561 | 55 | ISO 228-1 |
| 1/16 | NPT | 27 | 0.9407 | 7.950 | 60 | ASME B1.20.1 | |
| 1/16 | BSPT | 28 | 0.907 | 7.72 | 6.56 | 55 | ISO 7-1 |
| 1/16 | BSPP | 28 | 0.907 | 7.723 | 6.561 | 55 | ISO 228-1 |
| 1/2sources differ | BSP | 14 | 1.814 | 20.955 | 18.631 | 55 | ISO 228-1 |
| 1/2sources differ | NPT | 14 | 1.8143 | 21.3360 | 60 | ASME B1.20.1 | |
| 1/2 | BSPT | 14 | 1.814 | 20.96 | 18.63 | 55 | ISO 7-1 |
| 1/2 | BSPP | 14 | 1.814 | 20.955 | 18.632 | 55 | ISO 228-1 |
| 1/2 Inch BSP | BSP | 14 | 20.99 | ||||
| 1sources differ | NPT | 11 1/2 | 2.2087 | 33.4010 | 60 | ASME B1.20.1 | |
| 1¼ | NPT | 11½ | 2.20878 | 42.16 | 60 | ASME B1.20.1 | |
| 1 3/4 | BSPP | 11 | 2.309 | 53.746 | 50.789 | 55 | ISO 228-1 |
| 1/4sources differ | BSP | 19 | 1.337 | 13.157 | 11.445 | 55 | ISO 228-1 |
| 1/4sources differ | NPT | 18 | 1.4111 | 13.716 | 60 | ASME B1.20.1 | |
| 1/4 | BSPT | 19 | 1.337 | 13.16 | 11.45 | 55 | ISO 7-1 |
| 1/4 | BSPP | 19 | 1.337 | 13.157 | 11.445 | 55 | ISO 228-1 |
| 1/4 Inch BSP | BSP | 19 | 13.16 | ||||
| 1½ | NPT | 11½ | 2.20878 | 48.26 | 60 | ASME B1.20.1 | |
| 1¼ | BSP | 11 | 2.309 | 41.91 | 38.953 | 55 | ISO 228-1 |
| 1/8sources differ | BSP | 28 | 0.907 | 9.728 | 8.566 | 55 | ISO 228-1 |
| 1/8sources differ | NPT | 27 | 0.9407 | 10.287 | 60 | ASME B1.20.1 | |
| 1/8 | BSPT | 28 | 0.907 | 9.73 | 8.57 | 55 | ISO 7-1 |
| 1/8 | BSPP | 28 | 0.907 | 9.728 | 8.566 | 55 | ISO 228-1 |
| 1/8 Inch BSP | BSP | 28 | 9.7 | ||||
| 1½ | BSP | 11 | 2.309 | 46.803 | 44.846 | 55 | ISO 228-1 |
| 1 Inch BSP | BSP | 11 | 33.25 | ||||
| 10 | NPT | 8 | 3.1750 | 273.0500 | 60 | ASME B1.20.1 | |
| 12 | NPT | 8 | 3.1750 | 323.8500 | 60 | ASME B1.20.1 | |
| 2sources differ | BSP | 11 | 2.309 | 59.614 | 56.656 | 55 | ISO 228-1 |
| 2-1/2 | BSP | 11 | 2.309 | 75.184 | 72.226 | 55 | ISO 228-1 |
| 2-1/2 | NPT | 8 | 3.1750 | 73.0250 | 60 | ASME B1.20.1 | |
| 2 1/2 | BSPT | 11 | 2.309 | 75.18 | 72.23 | 55 | ISO 7-1 |
| 2 1/2 | BSPP | 11 | 2.309 | 75.184 | 72.227 | 55 | ISO 228-1 |
| 2 1/4 | BSPP | 11 | 2.309 | 65.710 | 62.753 | 55 | ISO 228-1 |
| 2sources differ | NPT | 11 1/2 | 2.2087 | 60.3250 | 60 | ASME B1.20.1 | |
| 2½ | NPT | 8 | 3.175 | 73.03 | 60 | ASME B1.20.1 | |
| 2 3/4 | BSPP | 11 | 2.309 | 81.534 | 78.577 | 55 | ISO 228-1 |
| 2½ | BSP | 11 | 2.309 | 75.184 | 72.227 | 55 | ISO 228-1 |
| 2 | BSPP | 11 | 2.309 | 59.614 | 56.657 | 55 | ISO 228-1 |
| 2 Inch BSP | BSP | 11 | 59.61 | ||||
| 3sources differ | BSP | 11 | 2.309 | 87.884 | 84.926 | 55 | ISO 228-1 |
| 3-1/2 | NPT | 8 | 3.1750 | 101.6000 | 60 | ASME B1.20.1 | |
| 3 1/2 | BSPP | 11 | 2.309 | 100.330 | 97.373 | 55 | ISO 228-1 |
| 3sources differ | NPT | 8 | 3.1750 | 88.9000 | 60 | ASME B1.20.1 | |
| 3/4sources differ | BSP | 14 | 1.814 | 26.441 | 24.117 | 55 | ISO 228-1 |
| 3/4sources differ | NPT | 14 | 1.8143 | 26.6700 | 60 | ASME B1.20.1 | |
| 3/4 | BSPT | 14 | 1.814 | 26.44 | 24.12 | 55 | ISO 7-1 |
| 3/4 | BSPP | 14 | 1.814 | 26.441 | 24.118 | 55 | ISO 228-1 |
| 3/4 Inch BSP | BSP | 14 | 26.44 | ||||
| 3 | BSPP | 11 | 2.309 | 87.884 | 84.927 | 55 | ISO 228-1 |
| 3/8sources differ | BSP | 19 | 1.337 | 16.662 | 14.950 | 55 | ISO 228-1 |
| 3/8sources differ | NPT | 18 | 1.4111 | 17.145 | 60 | ASME B1.20.1 | |
| 3/8 | BSPT | 19 | 1.337 | 16.66 | 14.95 | 55 | ISO 7-1 |
| 3/8 | BSPP | 19 | 1.337 | 16.662 | 14.950 | 55 | ISO 228-1 |
| 3/8 Inch BSP | BSP | 19 | 16.66 | ||||
| 4sources differ | BSP | 11 | 2.309 | 113.030 | 110.072 | 55 | ISO 228-1 |
| 4 1/2 | BSPP | 11 | 2.309 | 125.730 | 122.773 | 55 | ISO 228-1 |
| 4sources differ | NPT | 8 | 3.1750 | 114.3000 | 60 | ASME B1.20.1 | |
| 4 | BSPP | 11 | 2.309 | 113.030 | 110.073 | 55 | ISO 228-1 |
| 5 | NPT | 8 | 3.1750 | 141.3002 | 60 | ASME B1.20.1 | |
| 5 1/2 | BSPP | 11 | 2.309 | 151.130 | 148.173 | 55 | ISO 228-1 |
| 5 | BSP | 11 | 2.309 | 138.430 | 135.472 | 55 | ISO 228-1 |
| 5 | BSPP | 11 | 2.309 | 138.430 | 135.473 | 55 | ISO 228-1 |
| 5/8sources differ | BSP | 14 | 1.814 | 22.911 | 20.587 | 55 | ISO 228-1 |
| 5/8 | BSPP | 14 | 1.814 | 22.911 | 20.588 | 55 | ISO 228-1 |
| 5/8 Inch BSP | BSP | 14 | 22.99 | ||||
| 6 | BSP | 11 | 2.309 | 163.830 | 160.872 | 55 | ISO 228-1 |
| 6 | NPT | 8 | 3.1750 | 168.2750 | 60 | ASME B1.20.1 | |
| 6 | BSPP | 11 | 2.309 | 163.830 | 160.873 | 55 | ISO 228-1 |
| 7/8 | BSP | 14 | 1.814 | 30.201 | 27.877 | 55 | ISO 228-1 |
| 7/8 | BSPP | 14 | 1.814 | 30.201 | 27.878 | 55 | ISO 228-1 |
| 8 | NPT | 8 | 3.1750 | 219.0750 | 60 | ASME B1.20.1 | |
| 1 ¼ | BSP | 11 | 41.9 | ||||
| 1 ½ | BSP | 11 | 47.8 | ||||
| 1 | BSPT | 11 | 2.309 | 33.25 | 30.29 | 55 | ISO 7-1 |
| 2 | BSPT | 11 | 2.309 | 59.61 | 56.66 | 55 | ISO 7-1 |
| 3 | BSPT | 11 | 2.309 | 87.88 | 84.93 | 55 | ISO 7-1 |
| 4 | BSPT | 11 | 2.309 | 113.03 | 110.07 | 55 | ISO 7-1 |
| 5 | BSPT | 11 | 2.309 | 138.43 | 135.47 | 55 | ISO 7-1 |
| 6 | BSPT | 11 | 2.309 | 163.83 | 160.87 | 55 | ISO 7-1 |
| 1 ¼ | NPT | 11½ | 42.2 | ||||
| 1 ½ | NPT | 11½ | 48.3 | ||||
| 5/8 | NPT | 14 | 22.9 |
Where this came from
Every record above links the page it was taken from and quotes the sentence that states it. These are the 8 sources this dataset was assembled from.
- machiningdoctor.comhttps://www.machiningdoctor.com/charts/bsp/
- en.wikipedia.orghttps://en.wikipedia.org/wiki/National_pipe_thread
- lsengineers.co.ukhttps://www.lsengineers.co.uk/advice-centre/bsp-thread-sizes-explained
- amesweb.infohttps://amesweb.info/Screws/BSP-Thread-Chart.aspx
- en.wikipedia.orghttps://en.wikipedia.org/wiki/British_Standard_Pipe
- geminivalve.comhttps://www.geminivalve.com/bsp-thread-vs-npt-fitting/
- htsspares.comhttps://www.htsspares.com/blog/how-to/how-to-measure-your-bsp-fittings
- trimantec.comhttps://trimantec.com/blogs/t/thread-identification-guide
Machine-readable
- data.jsonThe whole dataset — every record with its source URL and source quote.
- Open Knowledge Format bundleOne JSON object per line — every record's frontmatter and quoted span exactly as it is held here, in one fetch.
- How this is made and checkedWhat "verified against source" does and does not mean.