Pressure-tight joints made on the pipe threads.
The standard ISO 7 - Pipe threads where pressure-tight joints are made on the threads consists of
- ISO 7-1:1994 Dimensions, tolerances and designation
- ISO 7-2:2000 Verification by means of limit gauges
The ISO 7 tapered Whitworth threads are equivalent to DIN 2999, BS 21 (BS EN 10226-1), JIS B0203.
Characteristics of ISO 7 tapered Withworth threads are
- tapered thread 1o47'
- truncation of roots and crests are rounded
- 55o thread angle
- pitch is measured in threads per inch
Note!
There is a distinction between
- jointing threads - sealing tapered/cylindrical threads for connections according to ISO 7-1 and/or EN 10226-1, BS 21
- fastening threads - not sealing parallel cylindrical threads for connections according to EN ISO 228-1
Diameter and pitches are the same for ISO 7-1 and ISO 228 threads.
ISO 7-1 is BSPT (R/Rp) – British Standard Tapered Pipe where
- R - tapered male with external threads
- Rp - cylindrical female with internal threads
- Rc - tapered female with internal threads
G-threads have a parallel shape in accordance with the DIN-EN-ISO 228-1 standard.
Both female Rp - internal cylindrical threads - and Rc - internal taper threads - are used in combination with male R - external threads - to make sealed joints. Male G-threads (parallel) can only be screwed into female G-threads.
Male R-threads (tapered) can be screwed into female G or R-threads.
For full table with Thread Tolerances - rotate the screen!
| Pipe Size (inches) | Threads per Inch P (TPI) | Lead p (mm) | Outside Diameter d = D (mm) | Pitch Diameter d2 = D2 (mm) | Minor Diameter d1 = D1 (mm) | Rp/Rc R | a | Tolerances of Internal Thread | Tolerances of External Thread | ||
|---|---|---|---|---|---|---|---|---|---|---|---|
(mm) | Pitch Diameter | turns | turns | (mm) | |||||||
| 1/16 | 28 | 0.907 | 7.723 | 7.142 | 6.561 | 1/16 | 4 | ± 0.071 | ± 1 1/4 | ± 1 | ± 0.9 |
| 1/8 | 28 | 0.907 | 9.23 | 9.147 | 8.566 | 1/8 | 4 | ± 0.071 | ± 1 1/4 | ± 1 | ± 0.9 |
| 1/4 | 19 | 1.337 | 13.157 | 12.301 | 11.445 | 1/4 | 6 | ± 0.104 | ± 1 1/4 | ± 1 | ± 1.3 |
| 3/8 | 19 | 1.337 | 16.662 | 15.806 | 14.950 | 3/8 | 6.4 | ± 0.104 | ± 1 1/4 | ± 1 | ± 1.3 |
| 1/2 | 14 | 1.814 | 20.955 | 19.793 | 18.631 | 1/2 | 8.2 | ± 0.142 | ± 1 1/4 | ± 1 | ± 1.8 |
| 5/8 | 14 | 1.814 | 22.911 | 21.749 | 20.587 | ||||||
| 3/4 | 14 | 1.814 | 26.441 | 25.279 | 24.117 | 3/4 | 9.5 | ± 0.142 | ± 1 1/4 | ± 1 | ± 1.8 |
| 7/8 | 14 | 1.814 | 30.201 | 29.039 | 27.877 | ||||||
| 1 | 11 | 2.309 | 33.249 | 31.770 | 30.291 | 1 | 10.4 | ± 0.18 | ± 1 1/4 | ± 1 | ± 2.3 |
| 1 1/8 | 11 | 2.309 | 37.897 | 36.418 | 34.939 | ||||||
| 1 1/4 | 11 | 2.309 | 41.910 | 40.431 | 38.952 | 1 1/4 | 12.7 | ± 0.18 | ± 1 1/4 | ± 1 | ± 2.3 |
| 1 1/2 | 11 | 2.309 | 47.803 | 46.324 | 44.845 | 1 1/2 | 12.7 | ± 0.18 | ± 1 1/4 | ± 1 | ± 2.3 |
| 1 3/4 | 11 | 2.309 | 53.746 | 52.267 | 50.788 | ||||||
| 2 | 11 | 2.309 | 59.614 | 58.135 | 56.656 | 2 | 15.9 | ± 0.18 | ± 1 1/4 | ± 1 | ± 2.3 |
| 2 1/4 | 11 | 2.309 | 65.710 | 64.231 | 62.752 | ||||||
| 2 1/2 | 11 | 2.309 | 75.184 | 73.705 | 72.226 | 2 1/2 | 17.5 | ± 0.216 | ± 1 1/2 | ± 1 1/2 | ± 3.5 |
| 2 3/4 | 11 | 2.309 | 81.534 | 80.055 | 78.576 | ||||||
| 3 | 11 | 2.309 | 87.884 | 86.405 | 84.926 | 3 | 20.6 | ± 0.216 | ± 1 1/2 | ± 1 1/2 | ± 3.5 |
The outside diameter of a pipe or fitting must be measured and compared to a table for size identification. A 3/4" ISO 7-1 pipe thread has an outside diameter - OD - of 1.060 inches. Each thread size has a defined number of threads per inch - TPI, or pitch. The 3/4" NPT pipe thread has 14 threads per inch. Both the TPI and OD of the thread are required for positive identification of thread size because more than one size have the same TPI.
ISO 7-1 threads may look similar to NPT threads. However, ISO and NPT threads should not be mixed. ISO threads have 55o taper angle versus 60o for NPT. The NPT root and crest configurations are also different from ISO. For ISO threads pitch is usually measured in millimeters ( may be expressed in Inch). The pitch are different.
Length of ISO 7-1 Thread to make a Tight Joint
| Nominal Pipe Size (inches) | Length of Thread (inches) |
|---|---|
| 1/8 | 0.27 |
| 1/4 | 0.39 |
| 3/8 | 0.41 |
| 1/2 | 0.53 |
| 3/4 | 0.55 |
| 1 | 0.66 |
| 1 1/4 | 0.68 |
| 1 1/2 | 0.68 |
| 2 | 0.70 |
| 2 1/2 | 0.93 |
| 3 | 1.02 |
| 4 | 1.09 |
| 5 | 1.19 |
| 6 | 1.21 |
DIN 2999 is the German version of BS 21 and BS 2779 which were the original British Whitworth screw thread pipe joint standards. DIN 2999 has been withdrawn, is obsolete and has been replaced with ISO 7 and ISO 228.
Related Topics
Dimensions of Pipes and Tubes
Pipe, tube and fittings sizes and dimensions. Inside and outside diameters, weights and more.Threads
Thread data - metric, unified, ACME and others.
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ANSI B1.20.1 - NPS - American National Standard Straight Pipe Threads
NPS pressure tight straight pipe threads with lubricant or sealer.ANSI B1.20.1 - NPT - American National Standard Taper Pipe Threads
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