Whitworth thread

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The Whitworth thread , also known as the inch thread , is named after Sir Joseph Whitworth who introduced it in 1841. It became the world's first standardized thread . In Germany this thread was standardized as DIN 11 and DIN 12 for a long time . It is still used today as British Standard Whitworth (BSW) and British Standard Fine (BSF) in Great Britain and as British standard pipe thread (BSP ) also in mainland Europe. In Germany it is still used as a pipe thread .

Cutting stock for Whitworth thread (approx. 1925)

Whitworth screw thread

Thread template for Whitworth threads

The Whitworth screw thread is the counterpart to the pointed thread for short, known as the metric thread. Both contain their outer diameter in the abbreviations: 14 ″ (inch thread, corresponds to 6.35 mm outer diameter) or M6 (metric thread, 6 mm outer diameter). In contrast to the pitch per revolution of the metric thread, the pitch is specified as the number of turns per inch of thread length: 14 "- 20 turns per inch (corresponds to 1.27 mm pitch); M6 (x1) - 1 mm pitch. Whitworth pointed thread has a 55 ° flank angle , metric 60 °.

The British standard of the Whitworth thread knows the types BSW (regular thread) and BSF ( fine thread ). For screws with an outside diameter of less than a quarter of an inch, it has been supplemented by the British Association Screw Thread .

In sound engineering, for example, a 38- inch BSW thread is used to screw microphone stands .

Whitworth pipe threads

12 ″ thread. The outside diameter (approximately 20 mm) corresponds to that of a 10 euro cent coin.

The Whitworth pipe thread is intended for screwing pipes (water, oil, gas, compressed air) and matching connecting parts ( fittings ). In sanitary , heating and air conditioning technology , it is usually cut as a conical thread on medium-weight and heavy threaded pipes according to DIN EN 10255 ( formerly DIN 2440, 2441 and 2442 ), which are available up to a size of 6 inches (DN 150) , from a size of 2 inches but are used less often than the preferred flange connections .

A distinction is made between tapered and cylindrical versions of Whitworth threads:

  • Tapered threads according to EN 10226 (old DIN 2999) are called "metallic sealing". A cylindrical internal thread with the "Rp ..." designation is generally combined with a tapered (conical) external thread with the "R ..." designation (see below ). A rare special case is the tapered (conical) internal thread with the “Rc ...” designation. The nominal diameter of the conical thread corresponds to that of the cylindrical mating thread after a few turns. With further tightening, the threads jam and press into one another and thus have a metallic seal. As a rule, such "R threads" are additionally provided with sealants such as liquid sealant , Teflon tape or cord or with sealing paste in connection with hemp as a sealant carrier before screwing in order to fill the remaining gaps. If hemp is used correctly, the connection can later be turned back a quarter turn without leaks.
  • Cylindrical threads according to ISO 228-1 (designation begins with "G ...", there used to be a risk of confusion because the associated thread was also designated with "R") are not metal-to-metal. They are to be provided with an additional metallic sealing surface or ring-shaped seal ( O-ring , O-ring , flat sealing ring ). The latter can, for example, be pressed outside the thread between the machined pipe end and a collar. This simplifies the installation. However, machined sealing surfaces (flat, conical or convex) are required.

Tapered R external threads can be screwed tightly into cylindrical G internal threads , as the same nominal dimensions apply. However, the cylindrical G internal thread according to ISO 228-1 only has positive dimensions, while EN 10226 (old DIN 2999) provides for positive and negative tolerances so that tapered R external threads screw into G internal threads about one thread turn further on average to let.

Origin of the customs declaration

The thread sizes specified in inches do not correspond to the respective outer diameter of the pipe (which is significantly larger than the specified inch dimension) or the thread. Originally, the inch size referred to the inside diameter of the cast iron pipes that were popular at the time. With an inner diameter of, for example, 12 "= 12.7 mm, they had an outer diameter of approximately 21 mm. With the introduction of better materials and manufacturing methods, the pipe wall thickness decreased. To ensure that the new pipes remained compatible with the existing tools and installations, the outside diameter was retained while the inside diameter increased, so that the size specifications in inches today neither correspond to the inside nor the outside diameter of the pipes.

Applications (selection)

House installation

Water installations (cold and hot water) are traditionally carried out in metallic sealing Whitworth pipe threads. Today, compatible plastic threads are sometimes used, but mostly soldered, pressed and other types of pipe connections .

Manufacturers of fittings and pipe fittings use the code letters listed below to indicate the intended pipe connections:

  • Rp - indicates a conical outer thread, followed by the size in inches
  • Rp - indicates a cylindrical internal thread, followed by the size in inches

Usual sizes are R 14 ″, R 38 ″, R 12 ″, R 34 ″, R1 ″, R1 14 ″, R1 12 ″ etc.


Depending on the air flow, the different sizes up to G3 ″ are used.

Scuba tank valve

In Europe, the (internal) thread G 58 ″ is used for compressed air in diving cylinder valves . In Germany, the M26x2 thread is required for Nitrox and Trimix fillings above 21% oxygen (O 2 ) - in practice, however, G 58 ″ is often used. Life-threatening mix-ups cannot be ruled out, the operator is liable in the event of damage .

Liquid cooler

Liquid coolers for power semiconductors, high-performance laser diodes or computer water cooling systems and their water / air heat exchangers use both conical and cylindrical Whitworth pipe threads. In Germany the G 14 ″ and the G 18 ″ thread are the most common, u. a. for computer cooling. In other countries, G 38 ″ or - especially in American countries - the local NPT thread (NPT: National Pipe Thread - US thread standard for pipe fittings) prevail.

Common Whitworth pipe threads

Dimension table of the most common Whitworth pipe threads (BSP) (for pipe diameter see under nominal diameter ):

  • Flank angle according to EN 10226-1 at right angles to the pipe axis: 55 °
  • G thread (cylindrical, not sealing) DIN 259 (ISO 228) (inside);
    • Identifier: G (e.g. G 1 ″) [to differentiate, e.g. T. IG (internal thread) and AG (external thread) common]
  • R thread (tapered, sealing up to 26 mm) EN 10226 (old DIN 2999) (ISO 7/1) Rp-R BS 21 (BSP-BSPT) taper 1:16;
    • Identifier external thread (conical): R (e.g. R 1 ″)
    • Identification internal thread (cylindrical): Rp (e.g. Rp1 ″) (not very common, new applications should be avoided)
in inches
per inch
Inside diameter Drill
(in mm)
(in mm)
(in mm)
(in mm)
G 116 28 06.561 06.843 06.80
G 18 28 08,566 08,848 08.80 9.728
G 14 19th 11.445 11,890 11.80 13.157
G 38 19th 14,950 15.395 15.25 16.662
G 12 14th 18.631 19,172 19.00 20.95
G 58 14th 20,587 21,128 21.00 22.91
G 34 14th 24.117 24.658 24.50 26.44
G 78 14th 27.877 28,418 28.25 30,201
G1 11 30.291 30.931 30.75 33.25
G1 18 11 34.939 35,579 35.30 37.897
G1 14 11 38,952 39,592 39.25 41.910
(G1 38 ) 11 41.365 42.005 41.70 44.323
G1 12 11 44.845 45.485 45.25 47,803
(G1 58 ) 11 49.030 49.670 49.50
G1 34 11 50.788 51.428 51.10 53.746
G2 11 56.656 57.296 57.00 59.61
G 2 14 11 62.752 63,392 63.10
(G 2 38 ) 11 66,440 67.080 66.90
G 2 12 11 72.226 72.866 72.60
G 2 34 11 78.576 79.216 78.90
G3 11 84,926 85.566 85.30

The table for tapered R threads is identical, with the difference that it has a taper ratio of 1:16.

Pipe thread according to standards
designation Profile sketch Flank
Short name a
Nominal size
(in inches)
according to standard application
cylindrical pipe thread
for connections not sealing in the thread
Whitworth thread.jpg 55 ° G G 1 12 A
G 1 12 B
116 … 6 ISO 228-1 External thread for pipes, pipe connections and fittings
G 1 12 Internal thread for fittings and armatures
G 34 34 , 1, 2 DIN 6630 External thread for barrel screw connections
without 5 12 5 12 DIN 6602 External thread for tank wagons
cylindrical pipe thread
for connections sealing in the thread
Rp Rp 12 116 … 6 DIN 2999-1 Internal thread for threaded pipes and fittings
Rp 18 18 1 12 DIN 3858 Internal thread for pipe fittings
Conical pipe thread
for connections that seal in the thread
Conical ratio to the pipe axis: 1:16 R. R 12 116 … 6 DIN 2999-1 External thread for threaded pipes and fittings
R 18 -1 18 1 12 DIN 2858 External thread for pipe fittings
a Complete designations are given in the relevant standards listed in the table.

Individual evidence

  1. ^ British Standard Whitworth in the English language Wikipedia
  2. ^ British standard pipe thread in the English language Wikipedia
  3. Information about pipes in sanitary, heating and air conditioning technology. In: Bosy-Online.de; "Sanitary-heating-air-conditioning information" by the central heating and ventilation master builder Bruno Bosy
  4. Notes on Withworth pipe threads at Heco.de
  5. The customs and the pipe at gewinde-normen.de
  6. Metal table book . Europa-Lehrmittel, 39th edition.