Ask any U.S. brigade chief about the most important fire-service equipment change of the last 30 years, and Storz couplings will be near the top of the list. The shift from threaded 4½” pumper-port connections to NFPA 1963 standardized 4″ and 5″ Storz couplings transformed how fire engines connect to hydrants — turning what was once a multi-turn, sometimes cross-threaded operation into a single quarter-turn lock that any firefighter can complete in seconds.

This guide explains what Storz couplings are, why NFPA 1963 standardized them in 1993, how 4″ and 5″ sizes compare, and what you need to specify when ordering LDH supply hose with Storz couplings for your apparatus.

What Is a Storz Coupling?

A Storz coupling is a quick-connect, threadless, sexless fire hose coupling. “Sexless” means there is no male and no female end — both ends are identical, so any two Storz couplings of the same size can connect to each other. The connection is made by pressing two couplings together so the hooked lugs slide into the opposing flanges, then rotating a quarter turn to lock the lugs into place.

The design was invented by Carl August Guido Storz in 1882, and patented in Switzerland and Germany shortly after. It became the European fire-service standard during the early 20th century. In the United States, Storz remained an obscure European import for almost a century until NFPA 1963 standardized 4″ and 5″ Storz dimensions in 1993, beginning the modern U.S. transition from threaded LDH couplings to Storz LDH.

NFPA 1963 — What the Standard Actually Covers

NFPA 1963: Standard for Fire Hose Connections is the governing U.S. document for fire hose couplings and adapters. Originally designated NFPA 194 (renumbered to 1963 in 1985), the standard covers couplings from ¾” (19 mm) through 8″ (200 mm) nominal size.

For threaded couplings, NFPA 1963 specifies the NH (National Hose) screw-thread dimensions that have been the U.S. fire-service standard for decades:

• 2.5-7.5 NH — 2½” attack hose thread (the dominant U.S. brigade attack coupling)
• 4.5-4 NH — 4½” pumper / steamer port thread (the traditional fire engine pump intake)
• 4-4 NH — 4″ supply hose thread
• 8-4 NH — 8″ large supply thread (added to NFPA 1963 in 2003 — rarely used in practice)

The 1993 edition of NFPA 1963 added a major new section: specifications for non-threaded (Storz) couplings in 4″ (100 mm) and 5″ (125 mm) sizes. This was the first time U.S. fire-service couplings were standardized at the non-threaded mating-surface level — ensuring that any 5″ Storz coupling from any manufacturer will connect with any other 5″ Storz coupling.

NFPA 1963 also specifies what every U.S. fire hydrant must have at minimum:

• Two 2½” attack ports with 2.5-7.5 NH threads
• One 4½” pumper (steamer) port with either 4.5-4 NH threads or a 5″ Storz port

The Storz alternative on the steamer port is the change that drove modern U.S. LDH practice. Most new hydrants installed since the late 1990s have a 5″ Storz steamer port; older hydrants can be retrofitted with a threaded-to-Storz adapter.

For full standards coverage including UL, FM, EN and international codes, see our Fire Hose Standards & Certifications guide.

4″ vs 5″ Storz — Side-by-Side Comparison

NFPA 1963 standardizes Storz in two sizes: 4″ (100 mm) and 5″ (125 mm). Which one is right for your apparatus depends on flow requirements, hydrant residual pressure, and apparatus storage constraints.

The numbers tell the story: a 5″ LDH supply line moves roughly 2.5× the water volume of a 4″ LDH at the same friction loss. For modern U.S. brigades operating heavy attack lines and large master streams, 5″ is the dominant choice. 4″ remains common in smaller departments where pump capacity is below 1,000 GPM, in areas with low hydrant residual pressure, and where the weight and bulk of 5″ is impractical.

For the full LDH product range from CA-FIRE — including both 4″ and 5″ Storz-coupled hose in rubber-covered through-the-weave construction and hydrant supply hose — see our dedicated product pages.

How a Storz Connection Works

The Storz design is mechanically simple — three components mate to create a watertight, pressure-rated connection:

1. Hooked lugs — Two or three projecting hooks at the mating face of each coupling. The lugs and flanges are arranged so that the same coupling can engage another identical coupling from any rotational angle.
2. Compression flanges — Cam surfaces opposite the lugs. As the couplings rotate a quarter turn relative to each other, the lugs slide along the flange cam surfaces, drawing the two faces together.
3. Storz gasket — A round-profile rubber gasket seated in a groove on each mating face. As the quarter turn compresses the faces together, the two gaskets crush against each other to form the watertight seal.

Most 4″ and 5″ Storz couplings have a locking detent or pin that engages when the coupling reaches the fully connected position. This prevents accidental disconnection under pressure — release the detent before rotating to disconnect, otherwise the coupling will hold even under significant hose movement.

Storz Material — Cast vs Forged Aluminum, Brass Options

Storz couplings are typically made of aluminum or brass. Within aluminum, the manufacturing method matters for safety-critical fire-service use:

• Forged aluminum is the recommended choice for fire-service LDH. The forging process aligns the metal grain structure along the load paths in the coupling, producing higher tensile strength and better fatigue resistance than cast aluminum at the same dimensions. The premium for forged Storz is worth it for safety-critical fire-fighting applications.
• Cast aluminum is acceptable for lower-pressure industrial water transfer (Camlock-style applications) but generally not recommended for safety-critical fire-service supply lines where the coupling must hold full hydrant pressure plus pump-residual surge.
• Brass Storz is heavier and more expensive than aluminum, but offers better corrosion resistance in marine and salt-exposure environments. Marine and offshore installations frequently specify brass Storz for this reason.

Storz Adapters — Connecting to Threaded Systems

If your apparatus uses Storz LDH but your hydrants still have threaded steamer ports — common in older municipal areas where hydrant replacement hasn’t kept pace with apparatus modernization — you’ll need adapters. The standard Storz adapter configurations:

• 5″ Storz × 4½” NH female — Adapts a 5″ Storz hose to a 4½” NH threaded hydrant steamer port. The most common adapter in U.S. fire service.
• 5″ Storz × 4½” NH male — Reverse direction. Adapts a 4½” threaded line to a 5″ Storz port on a modern hydrant or pump intake.
• 4″ Storz × 4″ NH female — For 4″ LDH connecting to a 4″ NH threaded port.
• 5″ Storz × 4″ Storz — Adapts between LDH sizes for departments transitioning equipment.
• 5″ Storz × 2½” NH male — Adapts a 5″ LDH to a 2½” attack line for direct hydrant-to-handline configurations.

Most modern U.S. apparatus carry a small set of Storz adapters in a hydrant tool bag on the rear bumper — typically a 5″ Storz × 4½” NH adapter plus a couple of attack-line adapters. CA-FIRE supplies the full adapter range alongside our LDH hose product line.

NFPA 1960 — The Coming 6″ Storz Standard

NFPA is currently consolidating multiple fire-hose standards (1931, 1936, 1961, 1963, 1964) into a single new standard, NFPA 1960. One of the major additions in NFPA 1960 is standardization of 6″ (150 mm) Storz couplings.

6″ LDH has been used informally in U.S. fire service for years — industrial fire protection, port-area service, refinery emergency response — but without NFPA standardization, the coupling dimensions varied by manufacturer. NFPA 1960 will lock 6″ Storz to a single standardized profile, enabling cross-manufacturer compatibility.

In the meantime, CA-FIRE supplies 6″ Storz couplings to the most widely accepted dimensions used in industrial fire-protection installations. Confirm coupling dimensions when ordering for cross-compatibility with existing systems.

Storz Outside the U.S. — International Compatibility

Storz is the dominant European fire-service coupling and is widely used in Australia. However, European Storz dimensions are not identical to NFPA 1963 Storz dimensions — and several near-identical coupling families coexist:

• NFPA 1963 Storz (4″ and 5″) — U.S. standard, the focus of this article.
• DIN Storz (A, B, C, D) — German DIN 14310 series in Storz sizes A (4″), B (2½”), C (1½”) and D (1″). DIN A is approximately 110 mm — different from NFPA 1963 4″ (100 mm), so the two are not directly compatible.
• Guillemin coupling (France, Belgium) — Similar quick-connect concept but with a different mating geometry. Used widely in France for fire service and wood-pellet delivery. Not interchangeable with Storz.
• Australian Storz — Generally compatible with European DIN Storz in most sizes.

If you’re ordering Storz couplings for use outside the U.S., specify the exact dimension standard required — DIN Storz, NFPA Storz, or your national fire-service equivalent. CA-FIRE supplies all major Storz variants from a single source.

What to Specify When You Order Storz-Coupled LDH

When ordering LDH supply hose with Storz couplings, six specifications determine the right product:

1. Hose ID: 4″ or 5″ (or 6″ for industrial). Match your apparatus pump capacity and area hydrant pressure.
2. Length per section: 50 ft or 100 ft typical. Longer continuous sections reduce coupling count and potential leak points.
3. Hose construction: Rubber-covered through-the-weave for maximum durability, or woven-jacket hydrant supply for lighter weight.
4. Storz dimension standard: NFPA 1963 (U.S.) is the default. Specify DIN, Australian or other if needed.
5. Coupling material: Forged aluminum (recommended for fire service), cast aluminum (industrial only), or brass (marine, salt exposure).
6. Adapter package: Include 5″ Storz × 4½” NH adapters for legacy hydrant compatibility. Plus 5″ Storz × 2½” NH for direct hydrant-to-attack scenarios.

Frequently Asked Questions

Why is Storz preferred over threaded couplings for LDH?

Storz connects in a single quarter-turn (about 1 second) versus 5-7 turns for a 4½” threaded coupling. Storz cannot cross-thread because there are no threads. The sexless design means any two Storz couplings of the same size can connect — no remembering which end is male vs female. And Storz has no exposed threads to be damaged when dropped or to cut firefighters’ hands during emergency response. For LDH supply where rapid hydrant connection is critical, Storz operational advantages are substantial.

Can I mix 4″ and 5″ Storz on the same apparatus?

Yes, but use adapters. 4″ Storz will not connect directly to 5″ Storz — different mating dimensions per NFPA 1963. A 5″ Storz × 4″ Storz adapter is the bridge for any apparatus running both sizes. Some departments carry both sizes — 5″ LDH for primary hydrant supply, 4″ LDH for relay pumping and supplemental supply. The adapter package is what makes the mixed configuration practical.

Are NFPA 1963 Storz and European DIN Storz compatible?

No, not directly. NFPA 1963 4″ Storz is 100 mm; DIN Storz A is approximately 110 mm. The two coupling families are dimensionally close but not interchangeable. If you operate equipment that must work in both U.S. and European environments, specify either NFPA 1963 dimensions or DIN dimensions consistently across the equipment package, and use adapters for the few connection points that span the two standards.

Why do Storz couplings sometimes leak — and how to fix it?

99% of Storz coupling leaks are gasket problems. The Storz gasket is a round-profile rubber ring seated in a groove on each mating face. Over time, the gasket compresses, hardens, cracks, or develops contamination on the sealing surface. Replacement is cheap (the gasket is a $1-3 part) and easy (pop out the old gasket, clean the groove, install new gasket). If gasket replacement doesn’t fix the leak, inspect the mating-face groove for nicks or dings that would prevent the gasket from seating properly. NFPA 1962 maintenance inspection should catch gasket wear before it becomes a leak. See our Fire Hose Testing & Inspection guide for the full inspection procedure.

Do I need a Storz spanner wrench?

Yes. Standard rocker-lug spanner wrenches don’t fit Storz coupling lugs — Storz lugs have a different profile. A dedicated Storz spanner wrench has a curved hook that engages the Storz lug, giving you the leverage to break the seal when disconnecting under pressure or when the gasket has stuck after a long deployment. Every Storz-equipped apparatus should carry at least one Storz spanner per LDH size in service.

Should I get forged or cast aluminum Storz couplings?

For fire-service LDH supply, specify forged aluminum. The forging process aligns the metal grain along the coupling’s load paths, producing significantly higher tensile strength and fatigue resistance than cast aluminum at the same dimensions. The price premium for forged Storz is modest, and the safety margin matters when the coupling is carrying full hydrant pressure plus pump-residual surge during a working fire. Cast aluminum Storz is acceptable for low-pressure industrial water transfer but not recommended for fire-service primary supply lines.