Types of screw threads : ISO | NPT | BSPT | JIS | Standards
NPT - PIPE THREAD The most common types of pipe thread are: • NPT - American Taper Pipe Thread = National Pipe Taper • NPTF - American Taper Pipe Thread for Dryseal joint without sealant compound = National Pipe Taper Fuel
NPT and NPTF appear to be identical. Both have the same pitch diameter at the top of the hole of the internal thread or end of the pipe on external threads and both have the same thread lengths or depths. However, there is a subtle difference in the root and crest diameters of the threads.
NPT / NPTF Thread size Major Diameter (mm) TPI 1/16” – 27 NPT 7,938 27 1/8” – 27 NPT 10,287 27 1/4” – 18 NPT 13,716 18 3/8” – 18 NPT 17,145 18 1/2” – 14 NPT 21,336 14 3/4” – 14 NPT 26,670 14 1” – 11 ½ NPT 33,401 11,5 2” – 11 ½ NPT 60,325 11,5
The flank angle is 60°. Female and Male thread are both tapered with equal angles.
NPT threads are also sometimes referred to as: • MIP (Male Iron Pipe) • FIP (Female Iron Pipe) • IPT (Iron Pipe Thread) • FPT (Female Pipe Thread) • MPT (Male Pipe Thread)
Note that these references are somewhat casual, and might possibly be used in reference to NPS instead of NPT Thread. NPS thread –National Pipe Straight- is not interchangeable with NPT thread.
G/R/RP - WHITWORTH THREAD (BSPP/BSPT) The most common types of whitworth thread are: • BSPP (G) – British Standard Pipe Parallel • BSPT (R/Rp) – British Standard Tapered Pipe, for pipes and tapered thread. An appropriate sealing compound can be used in the thread to ensure a leak-proof joint.
BSPP (G) Thread size (inch) Major Diameter (mm) Minor Diameter (mm) TPI G 1/16” 7,723 6,561 28 G 1/8” 9,728 8,566 28 G 1/4” 13,157 11,445 19 G 3/8” 16,662 14,950 19 G 1/2” 20,955 18,631 14 G 3/4” 26,441 24,117 14 G 1” 33,249 30,291 11 G 2” 59,614 56,656 11
BSPT (R/Rp) Male Thread size (inch)
Female Thread size (inch)
Major Diameter (mm)
Minor Female Diameter (mm)
TPI
R 1/16” Rp 1/16” 7,723 6,490 28 R 1/8” Rp 1/8” 9,728 8,495 28 R 1/4” Rp 1/4” 13,157 11,341 19 R 3/8” Rp 3/8” 16,662 14,846 19 R 1/2” Rp 1/2” 20,955 18,489 14 R 3/4” Rp 3/4” 26,441 23,975 14 R 1” Rp 1” 33,249 30,111 11 R 2” Rp 2” 59,614 56,476 11
The flank angle is 55°. BSPP: Female and Male thread are both parallel. BSPT: Female thread is parallel and male thread is tapered. - Female thread can also be tapered: Rc, but this is not common.