AN Fitting Washer / Nut
What Are AN Fitting Washers and Nuts?
When building or servicing a performance fluid system — whether it's fuel, oil, coolant, or hydraulic lines — the small pieces of hardware holding everything together matter just as much as the hose itself. AN fitting washers and nuts are the critical fastening and sealing components used throughout AN (Army-Navy) plumbing systems, ensuring connections stay tight and leak-free under real-world heat, vibration, and pressure.
AN fitting hardware originated as a military specification developed during World War II and was later adopted across motorsports and aviation before becoming a staple in street performance builds. The "AN" designation refers to a standardized system built around a 37-degree flare angle that creates a reliable metal-to-metal seal when the nut is properly torqued. The nut threads over the hose end and tightens onto the mating fitting, while washers — typically made from soft aluminum, copper, or fiber — are used at specific connection points to fill any gap and prevent fluid from weeping past the joint.
Why This Hardware Matters
A performance plumbing system is only as reliable as its weakest connection. AN nuts provide the clamping force that drives the flared hose end firmly into the seating cone of the fitting, forming a seal that is far more robust than a hose clamp or push-on connection. Sealing washers play an equally important role: they conform to microscopic surface imperfections between mating faces, ensuring a leak-free interface — especially on banjo-style fittings, carburetor inlet ports, and bulkhead pass-throughs where a gasket-like seal is required.
Because fuel system leaks can be dangerous, selecting the right washer material is key. Aluminum crush washers are common for general AN applications, while copper washers offer excellent conformability for harder mating surfaces, and fiber or rubber-backed washers are sometimes used on carbureted setups. Matching the correct AN size — whether -4AN, -6AN, -8AN, -10AN, or larger — is equally critical, as mismatched hardware can lead to cross-threading or incomplete sealing.
Key Considerations When Shopping
- Size compatibility: Always match your washer and nut to the correct AN dash size (-4, -6, -8, -10, etc.) used in your system.
- Material: Choose washer material based on the mating surface — aluminum for lightweight general use, copper for better conformability on harder surfaces.
- Bulkhead applications: Bulkhead fittings require both a securing nut and a sealing washer on each side of the panel; verify your hardware kit covers both.
- Reusability: Crush washers are typically single-use and should be replaced any time a fitting is disassembled to maintain a leak-free seal.
- Thread condition: Always inspect AN nuts for worn or damaged threads before reuse — a compromised nut can prevent the flare from seating correctly.
Top Brands in AN Fitting Washers & Nuts
For high-quality AN fitting hardware, Vibrant Performance is a trusted name among builders seeking reliable, precision-machined components at a practical price point. Vibrant offers a comprehensive range of AN fittings and associated hardware — including washers and nuts — machined from quality materials and engineered to work seamlessly with their full lineup of braided hoses, adapters, and hose ends. Their fittings are designed to deliver consistent performance across fuel, oil, coolant, and other fluid systems.