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Pipe thread identification guide
Thread Information
Abbreviation Name Threading Compatibility Seal method Other info
BSPP British Standard Pipe Parallel Male BSPP with Female BSPP.
Female BSPP with Male BSPP.
Female BSPP with Male BSPT.
Washer / O-Ring Used primarily for threaded ports and is similar to SAE straight thread. The male has straight threads and an o-ring. The BSPP female has straight threads and a sealing face.
BSPT British Standard Pipe Taper Male BSPT with Female BSPT.
Male BSPT with Female BSPP.
Thread
Washer
The British Standard pipe taper (BSPT) male has tapered threads. The BSPT female has tapered threads.
GHT Garden Hose Thread Male GHT with Female GHT.
Female GHT with Male GHT.
Washer Thread is the same for all hose sizes. Not compatible with other systems.
IPS Iron Pipe Straight Thread Generic name for straight pipe thread. Washer See NPSH for compatibility.
IPT Iron Pipe Thread Generic name for all pipe thread. more information required
JIC Joint Industrial Committee Used with other mating JIC threads Mechanical The JIC male has straight threads and a 37 degree flare seat. The JIC female has straight threads and a 37° flare seat. The seal is made on the 37° flare seat.
NH or NST National Hose thread also known as National Standard Thread Male NH-NST with Female NH-NST.
Female NH-NST with Male NH-NST.
Washer Popular on many fire hydrants and accessories. Thread pitch and diameters of fire threads may vary according to local regulations.
NPT National Pipe Tapered Male NPT and Female NPT.
Male NPT with Female NPSM.
Male NPT with Female NPSH.
Thread.
Washer.
Washer.
American Standard Taper Pipe Thread. Female NPT not compatible with Male NPSM or Male NPSH.
NPSH National Pipe Straight Hose Male NPSH and Female NPSH.
Female NPSH with Male NPT.
Female NPSH with Male NPSM.
Washer.
Washer.
Washer.
American Standard Straight Pipe for hose couplings.
NPSM National Pipe Straight Mechanical Male NPSM and Female NPSM.
Female NPSM with Male NPSH.
Female NPSM with Male NPT.
Seal can be either mechanical or washer. American Standard Straight Mechanical Joints.

NST - NH
A popular threaded connection on fire hydrants and equipment is NST - National Standard Thread, also known as National Hose Thread (NH). NST (NH) is not compatible with other thread types, so adapters are used to connect different types of couplings to an NST (NH) threaded connection.

NST (NH) threads have a different measurement than NPT and when people are unaware of this, they can order the wrong item. The following chart provides proper measurement information. NST - NH is a gasket sealed thread type and female couplings have a gasket. It's typically not necessary to use plumbers tape or thread sealant paste with this type of connection. If leakage is occuring, check or replace the gasket.

NST - NH Thread Dimensions
Thread
Type
Size
Threads
Per
Inch
Max. Outside
Diameter
of male
Min. Inside
Diameter
of female
NST (NH)
1 inch
8
1.375 inches
1.2246 inches
NST (NH)
1.5 inch
9
1.99 inches
1.8577 inches
NST (NH)
2.5 inch
7.5
3.068 inches
2.9104 inches
NST (NH)
3 inch
6
3.623 inches
3.5306 inches


NPSH
NPSH is a popular thread type on low pressure water suction and discharge hose couplings. NPSH is often mistaken for pipe thread because NPSH female couplings will connect to a Male NPT threaded connection. For example an NPSH female hose coupling will connect to a Male NPT pipe connection on a pump. NPSH is a gasket sealed thread and the female NPSH coupling will have a gasket. Pipe thread sealant and plumbers tape is typically not used with gasket sealed threads.

NPSH Thread Dimensions
Thread
Type
Size
Threads
Per
Inch
Max. Outside
Diameter
of male
Min. Inside
Diameter
of female
NPSH
0.5 inch
14
0.8248 inches
0.7395 inches
NPSH
0.75 inches
14
1.0353 inches
0.9500 inches
NPSH
1 inch
11.5
1.2951 inches
1.1921 inches
NPSH
1.25 inch
11.5
1.6399 inches
1.5369 inches
NPSH
1.5 inch
11.5
1.8788 inches
1.7758 inches
NPSH
2 inch
11.5
2.3528 inches
2.2498 inches
NPSH
2.5 inch
8
2.8434 inches
2.6930 inches


NPT
NPT is a popular thread type for many kinds of hose couplings, valves, pressure gauges and pipe fittings. Plumbers tape or thread sealing paste is recommended.

NPT Thread Dimensions
Thread
Type
Size
Threads
Per
Inch
Pipe
Outside
Diameter
NPT
1/8 inch
27
0.405 inches
NPT
0.25 inches
18
0.540 inches
NPT
3/8 inch
18
0.675 inches
NPT
0.5 inch
14
0.840 inches
NPT
0.75 inch
14
1.050 inches
NPT
1 inch
11.5
1.315 inches
NPT
1.25 inch
11.5
1.660 inches
NPT
1.5 inch
11.5
1.900 inches
NPT
2 inch
11.5
2.375 inches
NPT
2.5 inch
8
2.875 inches
NPT
3 inch
8
3.500 inches
NPT
4 inch
8
4.500 inches
NPT
5 inch
8
5.563 inches
NPT
6 inch
8
6.625 inches
NPT
8 inch
8
8.625 inches
NPT
10 inch
8
10.750 inches
NPT
12 inch
8
12.750 inches

SAE 45 degree flare
The SAE 45° flare male will mate with an SAE 45° flare female only. The SAE male has straight threads and a 45°; flare seat. The SAE female has straight threads and a 45° flare seat. The seal is made on the 45° flare seat.

SAE inverted flare
The SAE 45° inverted flare male will mate with a 42° inverted flare female only. The male has straight threads and a 45° inverted flare. The female has straight threads and a 42° inverted flare. The seal is made on the 45° flare seat on the male and the 42° flare seat on the female.

SAE straight thread o-ring boss
The o-ring boss male will mate with an o-ring boss female only. The female is generally found on equipment ports. The male has straight threads and an o-ring. The female has straight threads and a sealing face. The seal is made at the o-ring on the male and the sealing face on the female.

Metric Thread
The metric thread is similar to the SAE straight thread as the seal is created by an o-ring on the male creating a seal on the smooth face or surface of the female.

ORF Seal
The ORF seal system consists of a flat, finished surface on the female connector's flange and a recessed o-ring held in a circular groove on the male. The seal is created as the flange and o-ring make contact as the female nut screws onto the male thread. A secondary seal is made as the male connector is drawn into contact with the flange. The back-up seal also prevents extrusion of the o-ring under extreme pressure. ORF provides a better seal in high vibration, high impulse or high torque applications.