AN815-3D - AN Fitting Union

AN815-3D – AN Fitting Union

Available now on the Airparts.aero Marketplace.

Overview

The AN815-3D is a military-standard, straight union fitting designed to connect two fluid lines of the same size in aerospace and high-performance automotive systems. The "AN" designation signifies that it is manufactured to the Air Force/Navy Aeronautical Standard, which dictates the geometry, material, and performance of the fitting. Specifically, the AN815-3D is a union for a -3 (dash three) size tube, featuring a 37-degree flared seating surface on both ends. It is precision-machined from high-strength aluminum alloy and is a fundamental component for creating reliable, leak-free connections in fuel, oil, and hydraulic lines.

Key Features

• 37-Degree Flare Seal: Engineered with a 37° flared seating surface. This is the universal standard for aerospace fluid fittings, creating a highly reliable metal-to-metal seal when connected to a flared tube and a corresponding B-nut (sleeve and nut).
• High-Strength Aluminum Alloy: Machined from a solid piece of high-strength 2024-T851 aluminum alloy. This material provides an excellent combination of strength, light weight, and corrosion resistance for most aviation fluid applications.
• AN Standard Certified: Manufactured in strict accordance with AN/MS/AS standards, ensuring perfect interchangeability with any other standard AN fitting of the same size. This guarantees dimensional accuracy, thread quality, and material integrity.
• 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, identifying the fitting as being made from aluminum alloy.
• Precision Machined Threads: Features Class 3A external threads, which is the tightest tolerance for aerospace fasteners, ensuring a secure, vibration-resistant connection with the mating B-nut.

Technical Specifications

• Standard: AN815 (superseded by SAE-AS5194)
• Full Part Number: AN815-3D
• Component Type: Straight Union, Flared Tube
• Material: Aluminum Alloy, 2024-T851
• Finish: Blue Anodized
• Tube Size (Dash Size): -3 (for 3/16 inch Outside Diameter tubing)
• Thread Specification: 3/8-24 UNF-3A
• Flare Angle: 37° per side
• Hex Size: 7/16 inch

Aircraft Compatibility

The AN815-3D union is a universal component not specific to a single aircraft model. It is used in virtually all types of certified and experimental aircraft where 3/16" fluid lines are joined.

• Common Applications:
  • Fuel Systems: Joining sections of fuel lines from tanks to the fuel selector, and from the selector to the engine.
  • Hydraulic Systems: Connecting lines for brakes, landing gear, and flaps in light aircraft.
  • Oil Systems: Used in external oil cooler lines and instrument pressure lines.
  • Pitot-Static Systems: In some applications for joining pneumatic lines.

Applications

The AN815-3D fitting is designed for a single, crucial purpose:

• In-Line Tube Connection: Provides a straight, in-line connection between two separate pieces of flared 3/16" tubing, allowing for the assembly of complex fluid systems or for repairs to be made to existing lines.

Why Choose AN815-3D?

In aircraft fluid systems, there is zero tolerance for leaks. The AN flared fitting system is the time-tested global standard for achieving reliable, high-pressure seals. Using a genuine AN815-3D union guarantees that the fitting has the correct material strength, precise flare angle, and thread quality to create a dependable seal that will withstand pressure, temperature cycling, and vibration. Substituting with a non-certified or industrial fitting (such as a 45° flare fitting) is a dangerous practice that will lead to leaks and potential in-flight failures. For any A&P mechanic or aircraft builder, using certified AN hardware is the only way to ensure a safe and airworthy fluid system.

Order Your AN815-3D Fittings Now

Build and maintain your aircraft's fluid systems with the certified quality of genuine AN hardware. Visit Airparts.aero to order your AN815-3D flare unions today.

The sealing mechanism of the AN815-3D fitting relies on the principle of concentric cone sealing. When a B-nut is tightened, it draws a flared tube end onto the 37-degree cone of the AN815 union. The high clamping force creates a small, circular line of contact between the two surfaces. This concentrated force effectively "coins" the softer tube flare material against the harder fitting cone, creating an extremely reliable metal-to-metal seal capable of holding thousands of PSI. This design is superior to compression or pipe thread fittings as it is more resistant to vibration and can be disconnected and reconnected multiple times without compromising the seal's integrity (though inspection of the flare is always recommended). The "-D" suffix in the part number specifically denotes that the material is 2024 aluminum alloy, distinguishing it from steel ("J") or other materials.

Note: Always use a proper 37° flaring tool to prepare tubing for use with AN fittings. Ensure fittings are clean and free of debris before assembly. Tighten B-nuts to the specified torque value using a calibrated torque wrench and support the union with a second wrench to prevent twisting the line. Never use thread sealant on flared fittings.