Common types of pipe threads used in the piping industry

Thread Information
Threads of many different kinds are used for different purposes in piping components.
The following are the more common types of pipe threads used in the piping industry :

1. NPT Tapered Pipe Threads



NPT (National Pipe Tapered) is made to specifications outlined in ANSI B1.2.

2. NPTF (National Pipe Thread Dryseal) (made to specifications outlined in ANSI B1.20.3.) This piping end is also used on hydraulic and pneumatic equipment.

3. ISO 7/1 Tapered Pipe Threads



International Organization For Standards (ISO 7/1) Tapered (PT).   ISO tapered threads are equivalent to DIN 2999. BSP Tr, JIS B0203, R 1/8 and R 1/4 Keg. etc. In application ISO threads are used similar to NPT threads. However, care should be used that ISO and NPT threads are not mixed. ISO threads have a 55 deg angle versus 60 deg  for NPT. The root and crest configurations are different from NPT. Thread pitch is usually measured in millimeters but may be expressed in Inch. In most sizes the threads-per-inch are different.

4. ISO 228/1 Parallel Pipe Threads


(International Organization For Standards (ISO 228/1) Parallel (PF))
ISO Parallel threads are equivalent to DIN ISO 228/1, BSP PL, JIS B0202, G 1/8 and G 1/4 etc.

These pipe threads are similar in configuration to ISO 7/1 threads except there is no taper. Therefore do not work by thread interference like the tapered pipe threads of ISO 7/1 or NPT. A gasket, cutting face or O-Ring is normally used to seal the parallel female threaded component.

Comparison Chart

Pipe Threads

Nominal Size	Threads Per inch	Pipe O.D	Included Thread Angle	Pitch
1/16"	NPT/NPTF 27 ISO  28	.312" .312"	60 deg 55 deg	.037" .036"
1/8"	NPT/NPTF 27 ISO  28	.405" .402"	60 deg 55 deg	.037" .036"
1/4"	NPT/NPTF 18 ISO  19	.540" .532"	60 deg 55 deg	.0556" .053"
3/8"	NPT/NPTF 18 ISO  19	.675" .677	60 deg 55 deg	.0556" .053"
1/2"	NPT/NPTF 14 ISO  14	.840" .838"	60 deg 55 deg	.0714" .071"
3/4"	NPT/NPTF 14 ISO  14	1.050" 1.060"	60 deg 55 deg	.0714" .071"
1"	NPT/NPTF 11 1/2 ISO  11	1.315" 1.327"	60 deg 55 deg	.087" .091"
1 - 1/4"	NPT/NPTF 11 1/2 ISO  11	1.660" 1.669"	60 deg 55 deg	.087" .091"
1 - 1/2"	NPT/NPTF 11 1/2 ISO  11	1.900" 1.902"	60 deg 55 deg	.087" .091"
2"	NPT/NPTF 11 1/2 ISO  11	2.375" 2.374"	60 deg 55 deg	.087" .091"

basic table data from: Imex/edited by Maryland Metrics