B.S.P.T.

British Standard Pipe Thread


British Standard Pipe Thread 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.


A list of 16 thread sizes are defined by the standards, ranging from 1⁄16 Inch to 6 Inch. The size was originally based on the inner diameter measured in inches of a steel tube for which the thread was intended. This often causes confusion, as people think the size refers to the outside diameter of the male thread.

Two types of threads are used:

Parallel (straight) threads, British Standard Pipe Parallel thread (BSPP)

Taper threads, British Standard Pipe Taper thread (BSPT)

Just to confuse things, often the T in BSPT refers to Thread and doesn't indicate either Taper or Parallel.

The threadform follows the British Standard Whitworth standard


The table below shows dimensions for male threads.


Thread

Threads per inch

Pitch mm

Outside Diameter mm

Outside Diameter inches

1/16 Inch

28

0.907

7.723

0.304

1/8 Inch

28

0.907

9.728

0.383

1/4 Inch

19

1.337

13.157

0.518

3/8 Inch

19

1.337

16.662

0.656

1/2 Inch

14

1.814

20.995

0.825

5/8 Inch

14

1.814

22.991

0.902

3/4 Inch

14

1.814

26.441

1.041

1 Inch

11

2.309

33.249

1.309

1¼ Inch

11

2.309

41.910

1.650

1½ Inch

11

2.309

47.803

1.882

2 Inch

11

2.309

59.614

2.347

2½ Inch

11

2.309

75.184

2.96

3 Inch

11

2.309

87.884

3.46

4 Inch

11

2.309

113.030

4.45

5 Inch

11

2.309

138.430

5.45

6 Inch

11

2.309

163.830

6.45


This is a 1/2 Inch thread, you can count 14 threads in one inch.
Example of half inch BSP thread


An end view of a 1/2 Inch male thread
End view of half inch BSP thread


As the name of the sizing does not match the actual diameter, there can be some confusion over sizing. We have shown some pictures of two of the more popular sizes along side popular UK coins.

First, a half inch thread which is similar in size to a 1 penny coin.

Half inch BSP thread shown against 1p coin


Second, a three quarter inch thread which is similar in size to a 2 pence coin :
3/4 inch BSP thread shown against 2p coin


Typical uses and sizes are :

1/4 Inch - Compressed air connections

3/8 Inch - Oil line connections

1/2 Inch - Basin and sink taps, radiator inlets, old outside tap outlets

5/8 Inch - Old outside tap outlets (very rare)

3/4 Inch - Bath taps, washing machine inlet hose connections, modern outside tap outlets

1 Inch - Domestic heating boilers and hot water cylinders

1-1/4 Inch - Wash hand basin wastes (bathroom sink)

1-1/2 Inch - Kitchen sink wastes, bath wastes, toilet syphon outlets

2-1/4 Inch - Immersion water heater elements


A selection of "Black Iron" BSP fittings :

BSP fittings


A selection of plumbing fittings with BSP threads :

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All reasonable steps have been taken to ensure that information on this website is accurate, but we do not warrant that such information is accurate or complete.