Technical information / Threads and fittings / ISO 228-1
Thread standard
ISO 228-1 · G
Parallel pipe thread (G)
The CSV uses semicolons as separators. The link carries the selected size.
| Size | nthreads/in | Ppitch | dmajor | d2pitch | d1minor | h | r | Pipenominal | Pipe Ømajor dia. |
|---|---|---|---|---|---|---|---|---|---|
| G 1/16 | 28 | 0.907 | 7.723 | 7.142 | 6.561 | 0.581 | 0.125 | DN3 | — |
| G 1/8 | 28 | 0.907 | 9.728 | 9.147 | 8.566 | 0.581 | 0.125 | DN6 | 10.2 |
| G 1/4 | 19 | 1.337 | 13.157 | 12.301 | 11.445 | 0.856 | 0.184 | DN8 | 13.5 |
| G 3/8 | 19 | 1.337 | 16.662 | 15.806 | 14.950 | 0.856 | 0.184 | DN10 | 17.2 |
| G 1/2 | 14 | 1.814 | 20.955 | 19.793 | 18.632 | 1.162 | 0.249 | DN15 | 21.3 |
| G 5/8 | 14 | 1.814 | 22.911 | 21.749 | 20.588 | 1.162 | 0.249 | — | — |
| G 3/4 | 14 | 1.814 | 26.441 | 25.279 | 24.118 | 1.162 | 0.249 | DN20 | 26.9 |
| G 7/8 | 14 | 1.814 | 30.201 | 29.039 | 27.878 | 1.162 | 0.249 | — | — |
| G 1 | 11 | 2.309 | 33.249 | 31.770 | 30.292 | 1.479 | 0.317 | DN25 | 33.7 |
| G 1 1/8 | 11 | 2.309 | 37.897 | 36.418 | 34.940 | 1.479 | 0.317 | — | — |
| G 1 1/4 | 11 | 2.309 | 41.910 | 40.431 | 38.953 | 1.479 | 0.317 | DN32 | 42.4 |
| G 1 1/2 | 11 | 2.309 | 47.803 | 46.324 | 44.846 | 1.479 | 0.317 | DN40 | 48.3 |
| G 1 3/4 | 11 | 2.309 | 53.746 | 52.267 | 50.789 | 1.479 | 0.317 | — | — |
| G 2 | 11 | 2.309 | 59.614 | 58.135 | 56.657 | 1.479 | 0.317 | DN50 | 60.3 |
| G 2 1/4 | 11 | 2.309 | 65.710 | 64.231 | 62.753 | 1.479 | 0.317 | — | — |
| G 2 1/2 | 11 | 2.309 | 75.184 | 73.705 | 72.227 | 1.479 | 0.317 | DN65 | 76.1 |
| G 2 3/4 | 11 | 2.309 | 81.534 | 80.055 | 78.577 | 1.479 | 0.317 | — | — |
| G 3 | 11 | 2.309 | 87.884 | 86.405 | 84.927 | 1.479 | 0.317 | DN80 | 88.9 |
| G 3 1/2 | 11 | 2.309 | 100.330 | 98.851 | 97.373 | 1.479 | 0.317 | — | — |
| G 4 | 11 | 2.309 | 113.030 | 111.551 | 110.073 | 1.479 | 0.317 | DN100 | 114.3 |
| G 4 1/2 | 11 | 2.309 | 125.730 | 124.251 | 122.773 | 1.479 | 0.317 | — | — |
| G 5 | 11 | 2.309 | 138.430 | 136.951 | 135.473 | 1.479 | 0.317 | DN125 | 139.7 |
| G 5 1/2 | 11 | 2.309 | 151.130 | 149.651 | 148.173 | 1.479 | 0.317 | — | — |
| G 6 | 11 | 2.309 | 163.830 | 162.351 | 160.873 | 1.479 | 0.317 | DN150 | 168.3 |
Notes
- This table has been compiled by Emsal from the relevant standards. For the full text of the standard, refer to your national standards body.
- The thread does not seal: because the G thread is parallel, sealing is made with a gasket, O-ring or face seal. For joints that must seal on the thread, the taper ISO 7-1 (R / Rp) thread is used.
- The thread profile is 55° (Whitworth) with rounded crests and roots. Dimensions are basic values for internal and external threads; external threads have tolerance classes A (fine) and B.
- The size designation (e.g. G 1) comes from the nominal pipe size; it is not the major diameter of the thread (G 1 → Ø33.249 mm).
- Accuracy and currency are not guaranteed; use the current edition of the standard for design and purchasing decisions. How the library is compiled →
Dimension letters
| d | Major diameter | P | Pitch |
| d2 | Pitch diameter | n | Threads per inch |
| d1 | Minor diameter | h | Thread height |
| r | Crest and root radius |
Joint type and P&ID symbol
The G thread is cylindrical and does not seal; it only holds the two parts together. Sealing is made by a flat gasket or O-ring between the shoulder and the mating face.
female partmale part, pipegasket / sealing tapethread
- Place the gasket or O-ring on the shoulder of the male part.
- Screw the part in by hand and tighten with a spanner once the shoulder seats on the gasket.
- Do not wrap sealing tape on the thread; sealing is made at the gasket.
Used for unions, gauges, sensors and hoses, and wherever joints are taken apart. A G male thread can be screwed into an Rp female thread but will not seal on the thread.
P&ID: Threaded jointTwo short thin lines perpendicular to the pipeline. Symbol library →
Not to scale; proportions are indicative.
