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AN818-10D – Eaton Aeroquip Aerospace Fitting
Available now on the Airparts.aero Marketplace.
Overview
The AN818-10D is a military-standard coupling nut, a fundamental and flight-critical component of the AN/JIC 37-degree flared tube fitting system. Commonly referred to as a "B-nut," this fitting is engineered to be used in conjunction with a tube sleeve (AN819) to connect a flared tube to a male AN fitting. Manufactured by industry leaders like Eaton Aeroquip and specified across countless aircraft platforms, the AN818-10D is precision-machined from high-strength aluminum alloy. It is the primary component that provides the mechanical force to create a secure, high-pressure, metal-to-metal seal in aircraft fuel, oil, hydraulic, and pneumatic systems.
Key Features
- Creates High-Pressure Flare Seal: Its sole function is to apply the necessary clamping force to seal a flared tube and sleeve against a male 37-degree flare fitting. This creates a proven, highly reliable seal capable of withstanding high pressures and intense vibration.
- Lightweight Aluminum Alloy: The "D" suffix specifies that the nut is machined from a solid piece of high-strength 2024 aluminum alloy. This material provides an excellent combination of strength and light weight for most general aviation and transport fluid applications.
- Precision Machined Threads: Features Class 3B internal threads, the tightest tolerance for aerospace fasteners. This ensures a secure, vibration-resistant connection with the mating male fitting and allows for smooth, accurate torque application.
- AN Standard Certified: As a certified Air Force/Navy (AN) standard part, it guarantees perfect interchangeability with any other standard AN/MS/AS fitting of the same size. It is the superseding part for the legacy M83798/1-10 specification, ensuring full compliance and traceability.
- Blue Anodized Finish: Finished with a blue anodized coating per MIL-A-8625. This finish not only provides enhanced corrosion and wear resistance but also serves as the standard color code, immediately identifying the fitting as being made from aluminum alloy.
Technical Specifications
- Standard: AN818 (Nut, Coupling, Flared Tube)
- Full Part Number: AN818-10D
- Superseded Part Number: M83798/1-10
- Eaton Aeroquip P/N (Example): 816-10D
- Component Type: Coupling Nut ("B-Nut")
- Material (D): 2024 Aluminum Alloy
- Finish: Blue Anodized
- Tube Size (Dash Size): -10 (for 5/8 inch Outside Diameter tubing)
- Thread Specification: 7/8-14 UNF-3B
Aircraft Compatibility
The AN818-10D is a universal fluid fitting used on nearly every type of certified and experimental aircraft ever built that utilizes 5/8-inch fluid lines.
- Common System Applications:
- Fuel Systems: Connecting main fuel lines from tanks to selectors, and from pumps to the engine.
- Hydraulic Systems: Used for high-pressure hydraulic lines for landing gear, flaps, and brakes.
- Oil Systems: The standard nut for connecting external oil cooler lines and other lubrication system plumbing.
- Pneumatic & Instrument Lines: Connecting high-pressure pneumatic lines and instrument pressure lines.
Applications
The AN818-10D is the industry-standard component for completing a flared tube connection:
- Fluid System Plumbing: A fundamental building block for creating reliable, serviceable, and leak-proof fluid systems throughout an aircraft.
- Hose and Tube Assembly: Used to connect both rigid flared tubing and flexible hose assemblies (with flared hose ends) to other components.
Why Choose AN818-10D?
In aircraft fluid systems, where leaks can lead to catastrophic failures such as engine stoppage or loss of hydraulic control, the integrity of every fitting is paramount. The AN818-10D is manufactured and certified to a military standard, guaranteeing that it has the correct material strength, precise threads, and dimensional tolerances to create a dependable, high-pressure seal. Using non-certified, commercial-grade fittings (like automotive or plumbing fittings) can introduce parts with incorrect flare angles or poor thread quality, leading to leaks and potential system failure. For any airworthy installation, trust only certified AN/MS hardware.
Order Your AN818-10D Fittings Now
Ensure the integrity of your aircraft's critical fluid systems with certified AN-standard hardware. Visit Airparts.aero to order your AN818-10D coupling nuts today.
The AN818-10D B-nut is the active component that creates the seal in a 37-degree flared fitting assembly. The system consists of three parts: the male fitting (e.g., AN815 union), the B-nut (AN818), and a sleeve (AN819). A tube is flared to 37 degrees, and the B-nut and sleeve are slid over it. When the B-nut is threaded onto the male fitting and tightened, its internal chamfer applies a powerful, uniform pressure to the back of the sleeve. The sleeve, in turn, clamps the flared tubing directly against the 37-degree cone of the male fitting. This creates a small, circular line of contact where the immense pressure forms a highly reliable, metal-to-metal seal, capable of holding thousands of PSI.
Note: Installation must be performed by a certified A&P mechanic. The flared tube end should never have sealant applied. The B-nut threads should be lightly lubricated with the system fluid (e.g., clean hydraulic fluid or oil) before tightening. The nut must be tightened to the specified torque value using a calibrated torque wrench to achieve a proper seal without over-stressing the flare.
