Fire Hose & Pipe Thread Guide: NH, NST, NPSH, NPT & GHT Explained

Learn more about the different types of thread and how they connect.

Choosing the correct fire hose, water hose, or pipe thread can be confusing. NH, NST, NPSH, NPT, and GHT threads may look similar, but they are not always compatible.

This guide explains the most common hose and pipe thread types, how each one seals, where they are commonly used, and which threads can connect together. Whether you are connecting a fire hose, water pump, fire hydrant, suction hose, discharge hose, nozzle, or garden hose, identifying the correct thread is critical for a secure, leak-free connection.

Common Hose & Pipe Thread Abbreviations

Here are the common abbreviations you will see when selecting hose fittings, adapters, pumps, and other water-handling equipment:

• F - Female - The coupling with internal threads that fits over a male thread.

• M - Male - The coupling with external threads that fits inside a female thread.

• NH / NHT / NST - (National Hose / National Hose Thread / National Standard Thread) - Common names used for the same basic fire hose thread standard. This is one of the most common fire hose connection types in the United States.

• NPSH / IPT - (National Pipe Straight Hose / Iron Pipe Thread) - A straight thread commonly used on hose couplings and water-handling equipment.

• NPT - (National Pipe Thread Tapered) - A tapered pipe thread commonly used for plumbing, pumps, valves, and permanent piping connections.

• GHT - (Garden Hose Thread) - The standard thread found on most residential garden hoses and outdoor faucets, typically 3/4".

Important: Thread diameter alone does not determine compatibility. Two fittings may appear to be the same size but have different thread pitches or thread forms and may not connect correctly.

NH / NHT / NST

Quick Compatibility Reference Guide:

• NH/NST Male → NH/NST Female: Yes

• NPSH Male → NPSH Female: Yes

• NPT Male → NPT Female: Yes

• NPT Male → NPSH Female: Often yes, when nominal size and thread pitch correspond

• NPSH Male → NPT Female: No

• GHT Male → GHT Female: Yes

• NH/NST → NPSH: Adapter required

• NH/NST → NPT: Adapter required

• GHT → NH/NST: Adapter required

NH / NST / NHT

NH / NST / NHT Fire Hose Thread are commonly used terms for National Hose thread and are widely associated with fire hose fittings, fire hose nozzles, water pumps, and firefighting equipment.

NH/NST is a straight thread, meaning the thread diameter remains consistent rather than tapering along the connection.

How Does NH / NST Thread Seal?

Because the threads are straight, the threads themselves do not create the watertight seal.

Instead, the male fitting tightens against a rubber gasket inside the female coupling. Compression of this gasket creates the water seal.

What Thread Is Used on a Fire Hydrant?

Fire hydrant connections can vary by municipality and location. NST/NH is commonly used on fire hydrants, with 2.5" hose outlets being particularly common and larger pumper connections often found on hydrants as well.

However, some municipalities use regional or proprietary hydrant threads. Never assume that every fire hydrant uses the same thread.

NH / NST Compatibility:

• Male NH (NST) - Female NH (NST)

• Female NH (NST) - Male NH (NST)

Not directly compatible with NPSH, NPT, or GHT.

A suitable thread adapter is required when connecting NH/NST equipment to a different thread standard.

NPSH

NPSH – National Pipe Straight Hose Thread is another straight thread commonly found on water hoses, suction hoses, discharge hoses, pumps, and industrial water-handling equipment.

Although NPSH can look similar to NH/NST, the thread specifications are different. They should not be assumed to be interchangeable.

Like NH/NST, an NPSH hose coupling typically uses a rubber gasket in the female coupling to create the water seal.

NPSH vs. NST

One of the most important differences between NPSH and NST/NH is the thread pitch. Depending on the nominal size, the number of threads per inch (TPI) differs between the two standards.

This means an NST fitting and an NPSH fitting of the same nominal size may look similar but will not necessarily connect correctly.

NPSH Compatibility:

• Male NPSH - Female NPSH

• Female NPSH - Male NPSH

• Female NPSH can commonly accept a corresponding Male NPT connection of the same nominal size

This last combination is useful when connecting certain hose assemblies to pumps, valves, and piping equipment.

NPT

NPT – National Pipe Thread is one of the most common pipe thread standards used in the United States.

Unlike NH/NST and NPSH hose threads, NPT threads are tapered. The male and female threads become progressively tighter as they are threaded together.

NPT is commonly found on:

• Water pumps

• Pipe fittings

• Valves

• Plumbing

• Manifolds

• Tanks and water systems

• Industrial equipment

NPT is generally used where a more permanent or semi-permanent threaded connection is required rather than as a frequently disconnected fire hose coupling.

How Does NPT Thread Seal?

NPT connections rely on the interference created by the tapered threads rather than a rubber gasket at the face of the fitting.

A suitable PTFE thread seal tape or pipe thread sealant is typically used when assembling NPT connections to help produce a reliable, leak-resistant seal.

NPT Compatibility:

• Male NPT - Female NPT or NPSH in many corresponding sizes

• Female NPT - Male NPT

Not compatible:

• Female NPT → Male NPSH

• NPT → NH/NST without an appropriate adapter

• NPT → GHT without an appropriate adapter

GHT

GHT (Garden Hose Thread) is the standard connection used on most residential garden hoses, hose bibs, outdoor faucets, and many light-duty water accessories in the United States.

Standard GHT connections are 3/4" thread, even though the actual hose itself may have a different inside diameter.

For example, both a 5/8" garden hose and a 3/4" garden hose will typically use the same 3/4" GHT connection.

How Does Garden Hose Thread Seal?

Like NH/NST hose connections, GHT connections normally seal using a rubber washer inside the female fitting rather than relying on the threads themselves to create the seal.

GHT connections are commonly used around homes, farms, ranches, gardens, and properties. They can also be useful when adapting firefighting or water-transfer equipment to a standard garden hose water source.

Compatibility:

• Male GHT - Female GHT

• Female GHT - Male GHT

GHT is not directly compatible with NH/NST, NPSH, or NPT. An adapter is required to transition between these thread types.

Alpine offers a 3/4" Female GHT to 1" Male NST Adapter for connecting standard garden hose equipment to compatible 1" NST/NH equipment.

Thread Adapters and Couplings

In real-world applications, it is common to encounter different hose sizes and thread types at pumps, fire hydrants, water tanks, nozzles, valves, and other water sources.

Carrying a completely separate hose assembly for every possible connection is impractical. Fire hose thread adapters allow you to transition between different thread types, fitting sizes, and male/female connections using your existing equipment.

For example, the correct adapter can allow one hose assembly to connect to a water pump, fire hydrant, water tank, garden hose, nozzle, or another hose size.

This is particularly useful for wildland firefighting, property fire protection, farms, ranches, vineyards, water transfer, and emergency water systems, where the available water source may change.

Alpine offers a range of Made in USA aluminum hose and thread adapters for connecting different hose sizes and thread configurations.

• Male to Female Adapters

• Female to Female Adapters

• Male to Male Adapters

How Do I Know Which Fire Hose Thread I Have?

Do not identify a hose thread based only on the outside diameter of the fitting.

To correctly identify a thread, you may need to determine:

1. Male or female connection

2. Nominal fitting or hose size

3. Outside or inside thread diameter

4. Threads per inch (TPI)

5. Straight or tapered thread

6. Thread standard — NH/NST, NPSH, NPT, GHT, or another standard

If you are unsure which connection you have, compare the fitting dimensions and thread pitch with the manufacturer's specifications before attempting to connect the fittings.

Never force two threaded fittings together. If they do not thread together smoothly by hand, stop and verify the thread types. Forcing incompatible threads can damage the fittings and prevent a reliable water seal.

Need Help Finding the Correct Hose Thread Adapter?

If you need to connect a fire hose, water pump, hydrant, garden hose, nozzle, tank, or other water source and aren't sure which thread adapter you need, Alpine can help determine the correct connection.

Browse our fire hose adapters and fittings, or contact Alpine with the thread type, fitting size, and male/female configuration you need.

If you have any further questions about thread types or need helping finding the right thread for your needs, please don't hesitate to reach out. CONTACT US