British Standard Pipe Explained

British Standard Pipe (BSP) is a set of technical standards for screw threads that has been adopted internationally for interconnecting and sealing pipes and fittings by mating an external (male) thread with an internal (female) thread. It has been adopted as standard in plumbing and pipe fitting, except in North America, where NPT and related threads are used.

Types

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.

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. (In Europe, taper female pipe threads are not commonly used.)

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

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 h ≈ 0.6403P

Pipe thread sizes

At least 41 thread sizes have been defined, ranging from ¹⁄₁₆ to 18, although of these only 15 are included in ISO 7 and 24 in ISO 228.^{[2] [3] [4] [5]} 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" (plus/minus one thread pitch) from the small end of the thread. The taper is 1:16, 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 density (TPI)	Thread pitch	Major diameter	Minor diameter	Gauge length	Tapping drill
	28	NaN3NaN3	7.723disp=tableNaNdisp=table	6.561disp=tableNaNdisp=table	NaN1NaN1	6.6	6.8
	28	NaN3NaN3	9.728disp=tableNaNdisp=table	8.566disp=tableNaNdisp=table	NaN1NaN1	8.6	8.8
	19	NaN3NaN3	13.157disp=tableNaNdisp=table	11.445disp=tableNaNdisp=table		0.23671NaN1	11.5	11.8
	19	NaN3NaN3	16.662disp=tableNaNdisp=table	14.95disp=tableNaNdisp=table	NaN1NaN1	15.0	15.3
	14	NaN3NaN3	20.955disp=tableNaNdisp=table	18.631disp=tableNaNdisp=table		0.32141NaN1	18.7	19.1
	14	NaN3NaN3	22.911disp=tableNaNdisp=table	20.587disp=tableNaNdisp=table		0.32141NaN1	20.7	21.1
	14	NaN3NaN3	26.441disp=tableNaNdisp=table	24.117disp=tableNaNdisp=table	NaN1NaN1	24.2	24.6
	14	NaN3NaN3	30.201disp=tableNaNdisp=table	27.877disp=tableNaNdisp=table	NaN1NaN1	28.0	28.3
1	11	NaN3NaN3	33.249disp=tableNaNdisp=table	30.291disp=tableNaNdisp=table		0.40911NaN1	30.4	30.9
	11	NaN3NaN3	37.897disp=tableNaNdisp=table	34.939disp=tableNaNdisp=table		0.40911NaN1	35.1	35.5
	11	NaN3NaN3	41.91disp=tableNaNdisp=table	38.952disp=tableNaNdisp=table	NaN1NaN1	39.1	39.5
	11	NaN3NaN3	44.323disp=tableNaNdisp=table	41.365disp=tableNaNdisp=table	NaN1NaN1	41.5	42.0
	11	NaN3NaN3	47.803disp=tableNaNdisp=table	44.845disp=tableNaNdisp=table	NaN1NaN1	45.0	45.4
	11	NaN3NaN3	52.883disp=tableNaNdisp=table	49.926disp=tableNaNdisp=table	NaN1NaN1	50.1	50.5
	11	NaN3NaN3	53.746disp=tableNaNdisp=table	50.788disp=tableNaNdisp=table	NaN1NaN1	50.9	51.4
	11	NaN3NaN3	56.998disp=tableNaNdisp=table	54.041disp=tableNaNdisp=table	NaN1NaN1	54.2	54.6
2	11	NaN3NaN3	59.614disp=tableNaNdisp=table	56.656disp=tableNaNdisp=table	NaN1NaN1	56.8	57.2
	11	NaN3NaN3	65.71disp=tableNaNdisp=table	62.752disp=tableNaNdisp=table	NaN1NaN1	62.9	63.3
	11	NaN3NaN3	75.184disp=tableNaNdisp=table	72.226disp=tableNaNdisp=table	NaN1NaN1	72.4	72.8
	11	NaN3NaN3	81.534disp=tableNaNdisp=table	78.576disp=tableNaNdisp=table	NaN1NaN1	78.7	79.2
3	11	NaN3NaN3	87.884disp=tableNaNdisp=table	84.926disp=tableNaNdisp=table	NaN1NaN1	85.1	85.5
	11	NaN3NaN3	93.98disp=tableNaNdisp=table	91.022disp=tableNaNdisp=table	NaN1NaN1	91.2	91.6
	11	NaN3NaN3	100.33disp=tableNaNdisp=table	97.372disp=tableNaNdisp=table	NaN1NaN1	97.5	98.0
	11	NaN3NaN3	106.68disp=tableNaNdisp=table	103.722disp=tableNaNdisp=table	NaN1NaN1	103.9	104.3
4	11	NaN3NaN3	113.03disp=tableNaNdisp=table	110.072disp=tableNaNdisp=table	11NaN1	110.2	110.7
	11	NaN3NaN3	125.73disp=tableNaNdisp=table	122.772disp=tableNaNdisp=table	11NaN1	122.9	123.4
5	11	NaN3NaN3	138.43disp=tableNaNdisp=table	135.472disp=tableNaNdisp=table	NaN1NaN1	135.6	136.1
	11	NaN3NaN3	151.13disp=tableNaNdisp=table	148.172disp=tableNaNdisp=table	NaN1NaN1	148.3	148.8
6	11	NaN3NaN3	163.83disp=tableNaNdisp=table	160.872disp=tableNaNdisp=table	NaN1NaN1	161.0	161.5
7	10	NaN3NaN3	7.453NaN3	7.3223NaN3	NaN1NaN1	186.1	186.6
8	10	NaN3NaN3	8.453NaN3	8.3223NaN3	NaN1NaN1	211.5	212.0
9	10	NaN3NaN3	9.453NaN3	9.3223NaN3	NaN1NaN1	236.9	237.4
10	10	NaN3NaN3	10.453NaN3	10.3223NaN3	NaN1NaN1	262.3	262.8
11	8	NaN3NaN3	11.453NaN3	11.293NaN3	NaN1NaN1	287.0	287.6
12	8	NaN3NaN3	12.453NaN3	12.293NaN3	NaN1NaN1	312.4	313.0
13	8	NaN3NaN3	13.683NaN3	13.523NaN3	NaN1NaN1	343.6	344.2
14	8	NaN3NaN3	14.683NaN3	14.523NaN3	NaN1NaN1	369.0	369.6
15	8	NaN3NaN3	15.683NaN3	15.523NaN3	NaN1NaN1	394.4	395.0
16	8	NaN3NaN3	16.683NaN3	16.523NaN3	NaN1NaN1	419.8	420.4
17	8	NaN3NaN3	17.683NaN3	17.523NaN3	21NaN1	445.2	445.8
18	8	NaN3NaN3	18.683NaN3	18.523NaN3	21NaN1	470.6	471.2

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

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

G / R size	nut sizes	Corresponding pipe
				Wall
		3
	15	6	10.2	2
	19	8	13.5	2.3
	22 or 23	10	17.2	2.3
	27	15	21.3	2.6
	32	20	26.9	2.6
1	43	25	33.7	3.2
	53	32	42.4	3.2
	57	40	48.3	3.2
2	70	50	60.3	3.6
		65	76.1	3.6
3		80	88.9	4
4		100	114.3	4.5
5		125	139.7	5
6		150	168.3	5

ISO 7 (Pressure Tight threads)

The standard ISO 7 - Pipe threads where pressure-tight joints are made on the threads consists of the following parts:

• ISO 7-1:1994 Dimensions, tolerances and designation
• ISO 7-2:2000 Verification by means of limit gauges

ISO 228 (Non Pressure Tight Threads)

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

• AN thread
• British standard brass thread
• British Standard Whitworth
• Garden hose thread
• National pipe thread
• Panzergewinde
• Thread angle
• Threaded pipe

External links

• British Standard Pipe Parallel Thread Dimensions
• British Standard Pipe Taper Thread Dimensions
• BSP Thread Charts and Diagrams, showing dimensions of tubing and fittings
• ISO 7-1:1994
• ISO 7-2:2000
• ISO 228-1:2000
• ISO 228-2:1987
• Parallel pipe threads G
• Parallel pipe threads PF

Notes and References

1. Web site: BSPM = British Standard Pipe Mechanical. 14 July 2016.
2. Web site: Maryland Metrics thread data charts. maryland metrics. 14 July 2016. dead. 24 July 2018. https://web.archive.org/web/20180724110116/http://mdmetric.com/tech/thddat7.htm.
3. Web site: RoyMech: Pipe Threads. 14 July 2016. 22 July 2018. https://web.archive.org/web/20180722082552/http://www.roymech.co.uk/Useful_Tables/Flanges/Pipe_Threads.html. dead.
4. Web site: How to ID British (BSP) Threads. 20 November 2017.
5. Web site: BSP Thread data. www.practicalmachinist.com. 2 May 2012 . 2016-07-15.