British Standard Pipe

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

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

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

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.^[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" (plus/minus one thread pitch) 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
									R 95%	G 80%
(in)	(in^−1)	(mm)	(in)	(mm)	(in)	(mm)	(in)	(mm)	(mm)	(mm)
^1⁄16	28	0.907	0.3041	7.723	0.2583	6.561	^5⁄32	4.0	6.6	6.8
^1⁄8	28	0.907	0.3830	9.728	0.3372	8.566	^5⁄32	4.0	8.6	8.8
^1⁄4	19	1.337	0.5180	13.157	0.4506	11.445	.2367	6.0	11.5	11.8
^3⁄8	19	1.337	0.6560	16.662	0.5886	14.950	^1⁄4	6.4	15.0	15.3
^1⁄2	14	1.814	0.8250	20.955	0.7335	18.631	.3214	8.2	18.7	19.1
^5⁄8	14	1.814	0.9020	22.911	0.8105	20.587	.3214	8.2	20.7	21.1
^3⁄4	14	1.814	1.0410	26.441	0.9495	24.117	^3⁄8	9.5	24.2	24.6
^7⁄8	14	1.814	1.1890	30.201	1.0975	27.877	^3⁄8	9.5	28.0	28.3
1	11	2.309	1.3090	33.249	1.1926	30.291	.4091	10.4	30.4	30.9
1 ^1⁄8	11	2.309	1.4920	37.897	1.3756	34.939	.4091	10.4	35.1	35.5
1 ^1⁄4	11	2.309	1.6500	41.910	1.5335	38.952	^1⁄2	12.7	39.1	39.5
1 ^3⁄8	11	2.309	1.7450	44.323	1.6285	41.365	^1⁄2	12.7	41.5	42.0
1 ^1⁄2	11	2.309	1.8820	47.803	1.7656	44.845	^1⁄2	12.7	45.0	45.4
1 ^5⁄8	11	2.309	2.0820	52.883	1.9656	49.926	^5⁄8	15.9	50.1	50.5
1 ^3⁄4	11	2.309	2.1160	53.746	1.9995	50.788	^5⁄8	15.9	50.9	51.4
1 ^7⁄8	11	2.309	2.2440	56.998	2.1276	54.041	^5⁄8	15.9	54.2	54.6
2	11	2.309	2.3470	59.614	2.2306	56.656	^5⁄8	15.9	56.8	57.2
2 ^1⁄4	11	2.309	2.5870	65.710	2.4706	62.752	^11⁄16	17.5	62.9	63.3
2 ^1⁄2	11	2.309	2.9600	75.184	2.8435	72.226	^11⁄16	17.5	72.4	72.8
2 ^3⁄4	11	2.309	3.2100	81.534	3.0935	78.576	^13⁄16	20.6	78.7	79.2
3	11	2.309	3.4600	87.884	3.3435	84.926	^13⁄16	20.6	85.1	85.5
3 ^1⁄4	11	2.309	3.7000	93.980	3.5835	91.022	^7⁄8	22.2	91.2	91.6
3 ^1⁄2	11	2.309	3.9500	100.330	3.8335	97.372	^7⁄8	22.2	97.5	98.0
3 ^3⁄4	11	2.309	4.2000	106.680	4.0835	103.722	^7⁄8	22.2	103.9	104.3
4	11	2.309	4.4500	113.030	4.3335	110.072	1	25.4	110.2	110.7
4 ^1⁄2	11	2.309	4.9500	125.730	4.8335	122.772	1	25.4	122.9	123.4
5	11	2.309	5.4500	138.430	5.3335	135.472	1 ^1⁄8	28.6	135.6	136.1
5 ^1⁄2	11	2.309	5.9500	151.130	5.8335	148.172	1 ^1⁄8	28.6	148.3	148.8
6	11	2.309	6.4500	163.830	6.3335	160.872	1 ^1⁄8	28.6	161.0	161.5
7	10	2.540	7.4500	189.230	7.3220	185.979	1 ^3⁄8	34.9	186.1	186.6
8	10	2.540	8.4500	214.630	8.3220	211.379	1 ^1⁄2	38.1	211.5	212.0
9	10	2.540	9.4500	240.030	9.3220	236.779	1 ^1⁄2	38.1	236.9	237.4
10	10	2.540	10.4500	265.430	10.3220	262.179	1 ^5⁄8	41.3	262.3	262.8
11	8	3.175	11.4500	290.830	11.2900	286.766	1 ^5⁄8	41.3	287.0	287.6
12	8	3.175	12.4500	316.230	12.2900	312.166	1 ^5⁄8	41.3	312.4	313.0
13	8	3.175	13.6800	347.472	13.5200	343.408	1 ^5⁄8	41.3	343.6	344.2
14	8	3.175	14.6800	372.872	14.5200	368.808	1 ^3⁄4	44.5	369.0	369.6
15	8	3.175	15.6800	398.272	15.5200	394.208	1 ^3⁄4	44.5	394.4	395.0
16	8	3.175	16.6800	423.672	16.5200	419.608	1 ^7⁄8	47.6	419.8	420.4
17	8	3.175	17.6800	449.072	17.5200	445.008	2	50.8	445.2	445.8
18	8	3.175	18.6800	474.472	18.5200	470.408	2	50.8	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 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

G / R size	Typ. nut sizes	Corresponding pipe
		DN	OD		Wall
(in)	(mm)	(mm)	(mm)	(in)	(mm)
^1⁄16		3
^1⁄8	15	6	10.2	0.40	2
^1⁄4	19	8	13.5	0.53	2.3
^3⁄8	22 or 23	10	17.2	0.68	2.3
^1⁄2	27	15	21.3	0.84	2.6
^3⁄4	32	20	26.9	1.06	2.6
1	43	25	33.7	1.33	3.2
1 ^1⁄4	53	32	42.4	1.67	3.2
1 ^1⁄2	57	40	48.3	1.90	3.2
2	70	50	60.3	2.37	3.6
2 ^1⁄2		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 7

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

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

References

1. "BSPM = British Standard Pipe Mechanical". Retrieved 14 July 2016.
2. "Archived copy" (PDF). Archived from the original (PDF) on 2013-10-07. Retrieved 2013-12-27.
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

• British Standard Pipe Parallel Thread Dimensions
• British Standard Pipe Taper Thread Dimensions