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BSP Sizing Explained

BSP sizing can be confusing since the reference size does not relate to the physical measurement. 

For example a male thread which physically measures 26mm or just over 1" would logically be thought of as 1" BSP, but is not! This thread would be referred to as 3/4" BSP.

Us the table below to translate between BSP trade references  and  the physical measurement. 

BSP

Trade Size

Major Diameter

(Physical Measurement)

Inch

mm

1/8"

0.383

9.728

1/4"

0.518

13.157

3/8"

0.656

16.662

1/2"

0.825

20.955

3/4"

1.041

26.441

1"

1.309

33.249

1 ¼"

1.65

41.91

1 ½"

1.882

47.803

2"

2.347

59.614

2 ½"

2.96

75.184

3"

3.46

87.884

4"

4.45

113.03