BSP thread form stands for British Standard Pipe and is common in Australia and the commonwealth countries. It is based on trade size rather than actual diameter which can lead to some confusion when measuring ports.
There are two types of BSP threads;
- Parrallel (BSPP) - also known as G or Rp
- Tapered (BSPT) - also know as R or Rc
Both threads have the same pitch, angle (55 degrees) and shape (rounded peaks and valleys).
The below table gives the major and minor diameter for each BSP Trade Thread Size.
Trade Size
Threads per inch
Pitch
Major Diameter
Minor Diameter
Gage Length
Inch
mm
Inch
mm
Inch
Mm
Inch
mm
1/8
28
0.0357
0.907
0.383
9.728
0.3372
8.565
0.1563
3.97
1/4
19
0.0526
1.337
0.518
13.157
0.4506
11.445
0.2367
6.012
3/8
19
0.0526
1.337
0.656
16.662
0.5886
14.95
0.25
6.35
1/2
14
0.0714
1.814
0.825
20.955
0.7336
18.633
0.3214
8.164
3/4
14
0.0714
1.814
1.041
26.441
0.9496
24.12
0.375
9.525
1
11
0.0909
2.309
1.309
33.249
1.1926
30.292
0.4091
10.391
1 ¼
11
0.0909
2.309
1.65
41.91
1.5336
38.953
0.5
12.7
1 ½
11
0.0909
2.309
1.882
47.803
1.7656
44.846
0.5
12.7
2
11
0.0909
2.309
2.347
59.614
2.2306
56.657
0.625
15.875
2 ½
11
0.0909
2.309
2.96
75.184
2.8436
72.227
0.6875
17.463
3
11
0.0909
2.309
3.46
87.884
3.3436
84.927
0.8125
20.638
4
11
0.0909
2.309
4.45
113.03
4.3336
110.073
NPT
NPT stands for National Pipe Thread and is an American standard thread. It may also be reffered to as MPT , MNPT or NPT (M) for male external threads and FPT, FNPT or NPT(F) for female interal threads. A thread sealant must always be used to achieve a leak free seal (except for NPTF). It is also based on Trade Size rather than actual diameter (similar to BSP in this regard).
Both threads have the same pitch, angle (60 degrees) and shape (flat peaks and valleys).
The below table gives the Threads Per Inch, Pithc and Major Diameter for NPT Threads.
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