BSPT

British Standard Pipe Thread

The threaded part(s) of plumbing fittings are made to a British Standard Pipe Thread size (BSP).

BSP sizes don’t match up with what you would measure using a ruler, which can obviously cause some confusion.

For example a 3/4 inch BSP thread actually measures more like 1 Inch with a ruler

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

0.907mm

7.723mm

0.304″

1/8 inch

28

0.907mm

9.728mm

0.383″

1/4 inch

19

1.337mm

13.157mm

0.518″

3/8 inch

19

1.337mm

16.662mm

0.656″

1/2 inch

14

1.814mm

20.995mm

0.825″

5/8 inch

14

1.814mm

22.991mm

0.902″

3/4 inch

14

1.814mm

26.441mm

1.041″

1 inch

11

2.309mm

33.249mm

1.309″

1-1/4 inch

11

2.309mm

41.910mm

1.650″

1-1/2 inch

11

2.309mm

47.803mm

1.882″

2 inch

11

2.309mm

59.614mm

2.347″

2-1/2 inch

11

2.309mm

75.184mm

2.96″

3 inch

11

2.309mm

87.884mm

3.46″

4 inch

11

2.309mm

113.030mm

4.45″

5 inch

11

2.309mm

138.430mm

5.45″

6 inch

11

2.309mm

163.830mm

6.45″

Lots more information available at www.bspt.co.uk



 


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