Dimension table for parallel straight Whitworth pipe thread and tapered Whitworth pipe thread
There are two types of Whitworth pipe thread for connecting and sealing valves and fittings: The parallel, straight Whitworth pipe thread and the tapered Whitworth pipe thread. Here you will find dimension tables for these thread standards.
Not all pipe threads are the same
Since 1956 the formula 1 inch = 25.4 mm has been in force. Back then, the mass referred to the inner diameter. A pipe thread with 1 inch had a width of 25.4 mm which resulted in an outside diameter of approximately 33 mm for the steel quality of that time. These were the masses used for production.
In the meantime, "inch" pipe dimensions are metrically defined by standards. A tube with an outside diameter of approximately 33 mm is and remains a "1 inch tube". This standard also specifies the thread designation.
Basically, two Whitworth pipe thread types are distinguished for connecting and sealing fittings and valves:
- The tapered Whitworth pipe thread, which increases along the length of the thread and is designated with the letter R.
- The parallel straight Whitworth pipe thread, which has a constant diameter and is designated by the letter G.
We list international thread standards for you, however not conclusive.
Dimension table for the parallel, straight Whitworth pipe thread according to DIN ISO 228/DIN 259 BSPP British Standard Pipe Parallel
| Thread identification size inch | Inch diameter | Outside diameter ISO in mm | Diameter core hole ISO in mm | Pitch in mm |
|---|---|---|---|---|
G1/8" | 0.125 | 9.73 | 8.57 | 0.907 |
G1/4" | 0.250 | 13.16 | 11.45 | 1.337 |
G3/8" | 0.375 | 16.66 | 14.95 | 1.337 |
G1/2" | 0.500 | 20.96 | 18.63 | 1.814 |
G3/4" | 0.750 | 26.44 | 24.12 | 1.814 |
G1" | 1.000 | 33.25 | 30.29 | 2.309 |
G1 1/4 (5/4)" | 1.250 | 41.91 | 38.95 | 2.309 |
G1 1/2 (6/4)" | 1.500 | 47.80 | 44.85 | 2.309 |
G2" | 2.000 | 59.61 | 56.66 | 2.309 |
G2 1/2" | 2.500 | 75.18 | 72.23 | 2.309 |
G3" | 3.000 | 87.89 | 84.93 | 2.309 |
G4" | 4.000 | 113.03 | 110.07 | 2.309 |
G5" | 5.000 | 138.43 | 135.47 | 2.309 |
This cylindrical pipe thread is suitable for connections that are not sealed in the thread.
Dimension table for the tapered Whitworth pipe thread according to DIN EN 10226-1/DIN EN 10226-2/formerly DIN 2999
| Thread identification size inch | Nominal diameter pipe in mm | Outside diameter ISO in mm | Diameter core hole ISO in mm | Pitch in mm |
|---|---|---|---|---|
R(p)1/8" | 6 | 9.73 | 8.57 | 0.907 |
R(p)1/4" | 8 | 13.15 | 11.45 | 1.337 |
R(p)3/8" | 10 | 16.66 | 14.95 | 1.337 |
R(p)1/2" | 15 | 20.96 | 18.63 | 1.814 |
R(p)3/4" | 20 | 26.44 | 24.12 | 1.814 |
R(p)1" | 25 | 33.25 | 30.29 | 2.309 |
R(p)1 1/4 (5/4)" | 32 | 41.91 | 38.95 | 2.309 |
R(p)1 1/2 (6/4)" | 40 | 47.80 | 44.85 | 2.309 |
R(p)2" | 50 | 59.61 | 56.66 | 2.309 |
R(p)2 1/2" | 65 | 75.18 | 72.23 | 2.309 |
R(p)3" | 80 | 87.88 | 84.93 | 2.309 |
R(p)4" | 100 | 113.03 | 110.07 | 2.309 |
R(p)5" | 125 | 138.43 | 135.47 | 2.309 |
(R = external thread, Rp = internal thread)
Tapered threads according to DIN EN 10226-1/DIN EN 10226-2/formerly DIN 2999 are designated as metallic sealing. A cylindrical Rp internal thread is combined with a conical R external thread.
Did you know that tapered R male threads can be screwed into cylindrical G female threads in a sealing manner? It works because the same nominal dimensions apply. However, the cylindrical female G-thread according to DIN ISO 228/DIN 259 has only positive dimensions. Tapered threads to DIN EN 10226-1/DIN EN 10226-2/formerly DIN 2999 have positive and negative tolerances. Therefore, tapered R external threads can be screwed into cylindrical G internal threads on average about one thread turn further into cylindrical G internal threads.
Whenever you need assistance with pipe threads, valves and fittings, please contact us:+41 (0)41 780 22 22 or info@tri-matic.ch. We are happy to assist you!
more news
Quality that's got it all
