Source: https://www.valvesonline.com.au/references/threads/ThreadsBSPBSP 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 RpTapered (BSPT) - also know as R or RcBoth threads have the same pitch, angle (55 degrees) and shape (rounded peaks and valleys).

Trade SizeThreads per inchPitchMajor DiameterMinor DiameterGage Length

InchmmInchmmInchMmInchmm

1/8280.03570.9070.38309.7280.33728.5650.15633.97

1/4190.05261.3370.518013.1570.450611.4450.23676.012

3/8190.05261.3370.656016.6620.588614.950.256.35

1/2140.07141.8140.825020.9550.733618.6330.32148.164

3/4140.07141.8141.041026.4410.949624.120.37509.525

1110.09092.3091.309033.2491.192630.2920.409110.391

1 110.09092.3091.6541.911.533638.9530.512.7

1 110.09092.3091.882047.8031.765644.8460.512.7

2110.09092.3092.34759.6142.230656.6570.625015.875

2 110.09092.3092.9675.1842.843672.2270.687517.463

3110.09092.3093.4687.8843.343684.9270.812520.638

4110.09092.3094.45113.034.3336110.073

NPTNPT 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).Trade SizeThreads per inchPitchMajor Diameter (O.D)

InchmmInchmm

1/8270.037040.940820.40510.29

1/4180.055561.411220.54013.72

3/8180.055561.411220.67517.15

1/2140.071431.814320.84021.34

3/4140.071431.814321.05026.67

111 0.086962.208781.31533.40

1 11 0.086962.208781.66042.16

1 11 0.086962.208781.90048.26

211 0.086962.208782.37560.33

2 80.125003.175002.87573.03

380.125003.175003.50088.90

480.125003.175004.500114.30

BSP vs NPTNPT threads are common in the United States and a few other countries, BSP threads are widely used in many other countries. BSPT -British Standard Pipe Taper BSPP -British Standard Pipe Parallel NPT -National Pipe Taper NPS -National Pipe StraightWhile the actual specified outside diameters of American National Pipe differ slightly from those of British Standard Pipe, either thread may reliably be cut onto a pipe of its respective trade size. BSPT equivalent is NPT and BSPPs equivalent is NPS.Never swap threads if it is a high pressure application.NPT/NPS and BSP threads are not compatible due to the differences in their thread forms, and not just the fact that most sizes have a different pitch. NPT/NPS threads have a 60 angle and have flattened peaks and valleys (Sellers thread form) where as BSP threads have a 55 angle and have rounded peaks and valleys (Whitworth thread form).NPT and BSP thread pitches (threads per inch) are listed below. To determine pitch, use a thread gauge or count the number of threads that fall into a 1" span. Trade SizePitch (Threads per Inch)

NPT/NPSBSP

1/82728

1/41819

3/81819

1/21414

1414

111 11

1 11 11

1 11 11

211 11

2 811

3811

3 811

4811

5811

6811