BSP is BRITISH STANDARD PIPE                            Also known as Whitworth 55° Thread Form
BSPT is BRITISH STANDARD PIPE TAPER              Thread form per AS 1722.1, BS 21, ISO 7
BSPP is BRITISH STANDARD PIPE PARALLEL        Thread form per AS 1722.2, ISO 228

BSPT male threads seal against threads of fixed BSPT female. 
Contact is made on the flanks of the threads.
Use of a thread sealant is recommended for BSPT male to BSPT female connections.
Measure the BSPT male thread Outside Diameter (OD), and female thread Inside Diameter (ID) at the first full thread near the end of the fitting.

bspt thread diagram

 

 

BSPT & BSPP Threads Dimensions

BSPT & BSPP
SIZE

PITCH

BSPT MALE
THREAD OD

BSPT FEMALE
THREAD ID

BSPP MALE
THREAD OD

BSPP FEMALE

inch

TPI

mm

inch

inch

inch

mm

inch

mm

inch

1/8

28

9.5

0.37

0.38

0.38

8.4

0.33

8.6

0.34

1/4

19

12.8

0.50

0.51

0.51

11.2

0.44

11.9

0.47

3/8

19

16.3

0.64

0.65

0.65

14.7

0.59

15.2

0.60

1/2

14

20.4

0.80

0.82

0.82

18.3

0.72

19.1

0.75

5/8

14

22.5

0.89

0.90

0.90

20.6

0.81

20.8

0.82

3/4

14

25.9

1.02

1.04

1.04

23.9

0.94

24.6

0.97

1

11

32.6

1.28

1.30

1.30

29.7

1.17

30.7

1.21

1  1/4

11

41.1

1.62

1.64

1.64

38.6

1.52

39.4

1.55

1  1/2

11

47.0

1.85

1.88

1.88

44.5

1.75

45.5

1.79

2

11

58.6

2.31

2.34

2.34

56.4

2.22

57.4

2.26

2  1/2

11

74.1

2.92

2.95

2.95

71.9

2.83

72.6

2.86

3 –

11

86.6

3.41

3.46

3.46

84.6

3.33

85.4

3.36

Thread size refers to the nominal bore of the pipe.
Subtract approx. 1/4″ (6mm) from thread diameter measurement for nominal pipe size.
Pitch is Threads Per Inch (TPI).
“Gas”, “R” & “G” also refer to BSP.
“Male Iron (Pipe)” may be BSP or NPT.