British Standard Pipe

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For the 7-bit coded character set, see ISO/IEC 646.

The British Standard Pipe (BSP) is a family of standard screw thread types that has been adopted internationally for interconnecting and sealing pipe ends by mating an external (male) with an internal (female) thread and has been adopted as a standard scale used in plumbing fittings, except in the United States where NPT is the standard used.

Types[edit]

Two types of threads are distinguished:

  • Parallel (straight) threads, British Standard Pipe Parallel thread (BSPP; originally also known as[1] British Standard Pipe Fitting thread/BSPF and British Standard Pipe Mechanical thread/BSPM), which have a constant diameter; denoted by the letter G.
  • Taper threads, British Standard Pipe Taper thread (BSPT), whose diameter increases or decreases along the length of the thread; denoted by the letter R.
BSPT Pipe Threads.[2]

These can be combined into two types of joints:

Jointing threads
These are pipe threads where pressure-tightness is made through the mating of two threads together. They always use a taper male thread, but can have either parallel or taper female threads. (International standards require all female threads to be parallel.)
Longscrew threads
These are parallel pipe threads used where a pressure-tight joint is achieved by the compression of a soft material (such as an o-ring seal or a washer) between the end face of the male thread and a socket or nipple face, with the tightening of a backnut.

Thread form[edit]

The thread form follows the British Standard Whitworth standard:

  • Symmetrical V-thread in which the angle between the flanks is 55° (measured in an axial plane)
  • One-sixth of this sharp V is truncated at the top and the bottom
  • The threads are rounded equally at crests and roots by circular arcs ending tangentially with the flanks where r=0.1373P
  • The theoretical depth of the thread is therefore 0.6403 times the nominal pitch

Pipe thread sizes[edit]

At least 41 thread sizes have been defined, ranging from 116 to 18, although most of those are no longer included in current standards.[3][4][5][6] The size number was originally based on the inner diameter (measured in inches) of a steel tube for which the thread was intended, but contemporary pipes tend to use thinner walls to save material, and thus have an inner diameter larger than this nominal size. In the modern standard metric version, it is simply a size number, where listed diameter size is the major outer diameter of the external thread. For a taper thread, it is the diameter at the "gauge length" from the small end of the thread. The taper is 1 to 16, meaning that for each 16 units of measurement increase in the distance from the end, the diameter increases by 1 unit of measurement.

G / R
size
Thread
pitch
Major
diameter
Minor
diameter
Gauge
length
Tapping drill
Taper

thread

Straight

thread

(in) (in−1) (mm) (in) (mm) (in) (mm) (in) (mm) (mm) (mm)
116 28 0.907 0.3041 7.723 0.2583 6.561 532 4.0 6.60 6.80
18 28 0.907 0.3830 9.728 0.3372 8.566 532 4.0 8.60 8.80
14 19 1.337 0.5180 13.157 0.4506 11.445 .2367 6.0 11.50 11.80
38 19 1.337 0.6560 16.662 0.5886 14.950 14 6.4 15.00 15.25
12 14 1.814 0.8250 20.955 0.7335 18.631 .3214 8.2 18.75 19.00
58 14 1.814 0.9020 22.911 0.8105 20.587 .3214 8.2 21.00
34 14 1.814 1.0410 26.441 0.9495 24.117 38 9.5 24.25 24.50
78 14 1.814 1.1890 30.201 1.0975 27.877 38 9.5 28.25
1 11 2.309 1.3090 33.249 1.1926 30.291 .4091 10.4 30.40 30.75
1 18 11 2.309 1.4920 37.897 1.3756 34.939 .4091 10.4 35.50
1 14 11 2.309 1.6500 41.910 1.5335 38.952 12 12.7 39.00 39.50
1 38 11 2.309 1.7450 44.323 1.6285 41.365 12 12.7 41.75
1 12 11 2.309 1.8820 47.803 1.7656 44.845 12 12.7 45.00 45.25
1 58 11 2.309 2.0820 52.883 1.9656 49.926 58 15.9 49.50
1 34 11 2.309 2.1160 53.746 1.9995 50.788 58 15.9 51.00
1 78 11 2.309 2.2440 56.998 2.1276 54.041 58 15.9
2 11 2.309 2.3470 59.614 2.2306 56.656 58 15.9 56.75 57.00
2 14 11 2.309 2.5870 65.710 2.4706 62.752 1116 17.5 63.30
2 12 11 2.309 2.9600 75.184 2.8435 72.226 1116 17.5 72.80
2 34 11 2.309 3.2100 81.534 3.0935 78.576 1316 20.6 79.10
3 11 2.309 3.4600 87.884 3.3435 84.926 1316 20.6 85.50
3 14 11 2.309 3.7000 93.980 3.5835 91.022 78 22.2 91.00
3 12 11 2.309 3.9500 100.330 3.8335 97.372 78 22.2 97.75
3 34 11 2.309 4.2000 106.680 4.0835 103.722 78 22.2 104.0
4 11 2.309 4.4500 113.030 4.3335 110.072 1 25.4 110.5
4 12 11 2.309 4.9500 125.730 4.8335 122.772 1 25.4 123.0
5 11 2.309 5.4500 138.430 5.3335 135.472 1 18 28.6 136.0
5 12 11 2.309 5.9500 151.130 5.8335 148.172 1 18 28.6 148.5
6 11 2.309 6.4500 163.830 6.3335 160.872 1 18 28.6 161.5
7 10 2.540 7.4500 189.230 7.3220 185.979 1 38 34.9
8 10 2.540 8.4500 214.630 8.3220 211.379 1 12 38.1
9 10 2.540 9.4500 240.030 9.3220 236.779 1 12 38.1
10 10 2.540 10.4500 265.430 10.3220 262.179 1 58 41.3
11 8 3.175 11.4500 290.830 11.2900 286.766 1 58 41.3
12 8 3.175 12.4500 316.230 12.2900 312.166 1 58 41.3
13 8 3.175 13.6800 347.472 13.5200 343.408 1 58 41.3
14 8 3.175 14.6800 372.872 14.5200 368.808 1 34 44.5
15 8 3.175 15.6800 398.272 15.5200 394.208 1 34 44.5
16 8 3.175 16.6800 423.672 16.5200 419.608 1 78 47.6
17 8 3.175 17.6800 449.072 17.5200 445.008 2 50.8
18 8 3.175 18.6800 474.472 18.5200 470.408 2 50.8


These standard pipe threads are formally referred to by the following sequence of blocks:

  • the words, Pipe thread,
  • the document number of the standard (e.g., ISO 7 or EN 10226)
  • the symbol for the pipe thread type:
    • G, external and internal parallel (ISO 228)
    • R, external taper (ISO 7)
    • Rp, internal parallel (ISO 7/1)
    • Rc, internal taper (ISO 7)
    • Rs, external parallel
  • the thread size

Threads are normally right-hand. For left-hand threads, the letters, LH, are appended.

Example: Pipe thread EN 10226 Rp 2½

The terminology for the use of G and R originated from Germany (G for gas, as it was originally designed for use on gas pipes; R for rohr, meaning pipe.)

Pipe and fastener dimensions[edit]

G / R
size
Typ. nut
sizes
Corresponding pipe
DN OD Wall
(in) (mm) (mm) (mm) (in) (mm)
18 15 6 10.2 0.40 2
14 19 8 13.5 0.53 2.3
38 22 or 23 10 17.2 0.68 2.3
12 27 15 21.3 0.84 2.6
34 32 20 26.9 1.06 2.6
1 43 25 33.7 1.33 3.2
1 14 53 32 42.4 1.67 3.2
1 12 57 40 48.3 1.90 3.2
2 70 50 60.3 2.37 3.6
2 12 65 76.1 3.00 3.6
3 80 88.9 3.50 4
4 100 114.3 4.50 4.5
5 125 139.7 5.50 5
6 150 165.1 6.50 5

ISO 228[edit]

The standard ISO 228 - Pipe threads where pressure-tight joints are not made on the threads consists of the following parts:

  • ISO 228-1:2000 Dimensions, tolerances and designation
  • ISO 228-2:1987 Verification by means of limit gauges

See also[edit]

References[edit]

  1. ^ "BSPM = British Standard Pipe Mechanical". Retrieved 14 July 2016. 
  2. ^ http://www.colder.com/Portals/0/Library/Resources/Literature/WhitePapers/Documents/NPT_whitepaper.pdf
  3. ^ maryland metrics. "Maryland Metrics thread data charts". Retrieved 14 July 2016. 
  4. ^ "RoyMech: Pipe Threads". Retrieved 14 July 2016. 
  5. ^ "How to ID British (BSP) Threads" (PDF). Retrieved 14 July 2016. 
  6. ^ "BSP Thread data". www.practicalmachinist.com. Retrieved 2016-07-15. 

External links[edit]