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Thread Sizes

BSPT & BSPP Threads

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 & 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.

NPT & NPS Threads

NPT is NATIONAL PIPE TAPER (AMERICAN):
Thread form per ANSI/ASME B1.20.1 

NPS is NATIONAL PIPE STRAIGHT (PARALLEL)     
Thread form per ANSI/ASME B1.20.1 

NPTF is NATIONAL PIPE TAPER FOR FUEL 
Thread form per SAE J476 

NPSM is NATIONAL PIPE STRAIGHT MECHANICAL   
Thread form per ANSI/ASME B1.20.1

National Pipe threads are similar in function to BSP threads, but are not generally interchangeable.
NPTF threads (also known as Dryseal) are an improvement to NPT.

Controlled truncation of threads mean the metal-to-metal thread seal is at root and crest of threads, in addition to flanks of threads.
Use of thread sealant is recommended for NPT male and NPT female connection.

Male thread Outside Diameter (OD), and female thread Inside Diameter (ID) are measured at the first full thread near end of the fitting.

NPT Threads Dimensions

NPT

NPT THREAD
SIZE

PITCH

MALE THREAD OD

FEMALE
THREAD ID

 inch

TPI

mm

inch

 mm

inch

1/8

27

 9.9

 0.39

8.4

 0.33

 1/4

18

13.2

 0.52

 11.2

0.44

3/8

18

 16.6

 0.65

14.7

0.58

1/2

14

20.6

0.81

17.8

0.70

3/4

14

26.0

1.02

23.4

0.92

1

11.5

32.5

1.28

29.5

1.16

1  1/4

11.5

41.2

1.62

38.1

1.50

1  1/2

11.5

47.3

1.86

43.9

1.73

2

11.5

59.3

2.33

56.4

2.22

2  1/2

8

71.5

2.82

69.1

2.72

3

8

87.3

3.44

84.8

3.34

NPSM

NPSM THREAD
SIZE

PITCH

FEMALE
THREAD ID

inch

 TPI

mm

inch

1/8

27

8.6

0.34

1/4

18

11.9

0.47

3/8

18

15.0

0.59

1/2

14

19.1

0.75

3/4

14

24.6

0.97

1

11.5

30.5

1.20

1  1/4

11.5

39.4

1.55

1  1/2

11.5

45.5

1.79

2

11.5

57.4

2.26

2  1/2

8

68.8

2.71

3

8

84.6

3.33

Thread size refers to the nominal bore of the pipe.
Subtract approximately 1/4” (6 mm) from thread measurement for nominal pipe size.
Pitch is Threads Per Inch (TPI).

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