NH & Pin Lug Couplings

An NH coupling (National Hose coupling) is an American-standard fire hose fitting that uses NHT (National Hose Thread) — also known as NST (National Standard Thread) — to connect fire hose, nozzles, appliances and other fire equipment. The NHT thread is a coarse, acme-form thread specified by NFPA 1963 (Standard for Fire Hose Connections) and ANSI/ASME B1.20.7.

NH couplings are the universal fire hose connection standard throughout the United States — every fire hydrant outlet, building standpipe, sprinkler system test drain, fire truck pump discharge and attack hose nozzle connection uses NHT. The NH system is also widely used in Canada, Mexico, the Philippines, South Korea, Taiwan, Thailand and other countries that have adopted American fire service standards.

The NH coupling is a swivel-type connection: the female half has a rotating swivel nut with internal NHT; the male half has a fixed shank with external NHT. They connect by rotating the swivel nut over the male shank, typically 3–5 turns for smaller sizes. CA-FIRE manufactures NH couplings from 1½" to 6" in aluminium, brass and polypropylene. The full coupling range covers all major international standards.

Both NH and pin lug couplings use National Hose Thread (NHT) and are dimensionally compatible — a standard NH male shank connects to a pin lug female swivel nut of the same size, and vice versa. The difference is in how the swivel nut is turned to make up the coupling:

Standard NH coupling: the swivel nut has a smooth outer surface, typically hexagonal or knurled. It is turned by hand or with standard tools. Simple and fast for small sizes (1½" to 2½") where hand-tightening is easy.

Pin lug coupling: the swivel nut has two or more external pins (lugs) on its outer face. A spanner wrench with matching holes engages the pins to provide mechanical advantage, making it easier to achieve proper torque on large-bore couplings (2½" and above) where hand-tightening is difficult — especially when wearing fire PPE gloves or working in contaminated environments. The spanner wrench engagement also allows the coupling to be tightened and broken loose mechanically, which is important on large suction hose where thread galling can otherwise make separation difficult.

In practice, 1½" and 1¾" attack hose uses standard NH couplings; 2½" attack hose and larger supply and suction hose commonly uses pin lug couplings in the US fire service.

Yes — NH (National Hose), NHT (National Hose Thread) and NST (National Standard Thread) all refer to the same thread form. The terminology varies by era, region and document: older US fire service literature uses "NH" or "NHT"; NFPA 1963 uses "NH"; ANSI/ASME B1.20.7 uses "NH"; and some jurisdictions and equipment manufacturers use "NST." All three terms describe the same acme-form coarse thread used on American fire hose couplings and hydrant connections.

This can cause confusion when specifying equipment or ordering parts internationally. If a specification calls for "NST couplings," it means the same as "NH couplings" or "NHT couplings." CA-FIRE NH couplings conform to NFPA 1963 / ANSI/ASME B1.20.7 NH thread dimensions and are compatible with all NH/NHT/NST-compliant equipment regardless of the terminology used in the specification.

Aluminium NH couplings are the standard choice for fire service use. Lightweight, corrosion-resistant in fresh water service, and available in the full size range 1½" to 6". CA-FIRE aluminium NH couplings are cast aluminium, dimensionally verified to NHT thread gauge. Anodising available on request.

Brass NH couplings are specified for corrosion-critical applications — seawater, coastal installations, chemical plants and potable water systems. Heavier than aluminium but significantly more corrosion-resistant in saline and chlorinated environments. Recommended for permanently installed connections on offshore platforms, marine fire systems and building fire hose cabinets in coastal areas.

Polypropylene (PP) NH couplings are the economy option for budget-sensitive applications — volunteer fire brigades, civil defence, agricultural and wildfire suppression. PP is the lightest option, significantly cheaper than aluminium or brass, and suitable for fresh water use at standard 16 bar working pressures. Not recommended for elevated temperatures, foam concentrate service or high-impact industrial environments. Available in 1½", 2½" and 3" sizes.

All three materials use the same NHT thread form and are interchangeable — a PP female swivel will connect to a brass male shank of the same NH size, and vice versa.

NH to BSP thread: CA-FIRE manufactures NH female × BSP male (NHF/BSP) and NH male × BSP female (NHM/BSP) adaptors in 1½" to 4" sizes in aluminium and brass. These allow NH-coupled hose to connect to BSP-threaded pump outlets, nozzles and building system connections — the most common requirement when NH-standard hose must interface with non-American equipment.

NH to Storz: NH and Storz couplings use different connection geometries and are not directly compatible. A mixed NH × Storz adaptor — NH coupling on one end, Storz coupling on the other — is available from CA-FIRE on request for projects requiring compatibility between American-standard and European-standard hose, common on international fire tender projects and multinational industrial facilities.

NH to Gost / BS336 / DSP: Similarly, NH × Gost, NH × BI and NH × DSP mixed adaptors are available on request. For projects requiring multi-standard compatibility across American, European and other national standards, CA-FIRE can manufacture a complete mixed-adaptor schedule to a project specification. Contact our sales team with your requirements.

To receive an accurate quotation, please provide the following when contacting CA-FIRE:

1. Coupling type — NH hose tail (NHT), NH × BSP thread adaptor (NHF/NHM), NH blank cap (NHC), NH reducer (NHRED), pin lug hose tail (PLT).
2. Size — 1½", 1¾", 2", 2½", 3", 4", 4½", 5" or 6" (NH); 2½", 3", 4", 4½", 5" or 6" (pin lug).
3. Gender — female swivel (F) or male shank (M) for hose tail couplings and thread adaptors.
4. Hose tail bore — internal diameter of the fire hose in mm (for hose tail couplings).
5. Thread spec — BSP size for thread adaptors (G1½", G2½", G3", G4").
6. Material — aluminium (AL), brass (BR) or polypropylene (PP).
7. Quantity — pieces per line item.
8. Special requirements — mixed-standard adaptors, anodising, test certificates, OEM packaging.

Contact CA-FIRE at sales@ca-fire.com, via WhatsApp, or via the contact page. Response within 24 hours.