AN815-3D - 3/16" Aluminum Alloy Flared Tube Union

AN815-3D – Flared Tube Union, 3/16" Aluminum Alloy

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The AN815-3D is a standard AN (Army-Navy) hydraulic fitting, a union specifically designed to connect two 3/16-inch flared tube ends in a straight line. This component is manufactured in strict accordance with military standards from high-strength 2024 aluminum alloy, as designated by the "D" suffix. It is a foundational component in low-to-medium pressure (up to 1500 PSI) fluid systems, used extensively in general aviation and older transport category aircraft for hydraulic, fuel, oil, and pneumatic applications.

The AN815-3D features a 37° male conical sealing surface on both ends. The seal is not created by the threads, but by the precise, high-pressure, metal-to-metal contact between this conical surface and the flared end of the mating tube. The entire fitting is anodized blue, which provides a durable, corrosion-resistant finish and serves as the standard color code for identifying aluminum alloy fluid fittings, preventing dangerous misapplication with steel components in high-pressure systems.

Key Features

• Army-Navy (AN) Specification Certified: Guarantees that the fitting meets the stringent material, dimensional, and quality control requirements for certified aircraft use.

• 37° Flared Tube Sealing Surface: The industry-standard geometry for creating a reliable, reusable, metal-to-metal seal in aircraft fluid systems.

• High-Strength 2024 Aluminum Alloy: Offers an excellent strength-to-weight ratio, ideal for airframe plumbing applications where weight is a critical factor.

• Anodized Blue Finish: Provides a hard, corrosion-resistant surface (per MIL-A-8625) and positively identifies the fitting as an aluminum alloy component.

• For 1500 PSI Systems: Engineered for reliable performance in standard low-to-medium pressure aircraft fluid power and transfer systems.

Technical Specifications

• Part Number: AN815-3D

• Component Type: Union, 37° Flared Tube

• Governing Specification: AN815 (now may be referenced under AS5175).

• Material: 2024 Aluminum Alloy.

• Finish: Anodized Blue per MIL-A-8625, Type II.

• Tube Size: For 3/16 inch OD tubing.

• Thread Size: 3/8-24 UNF on both ends.

• Nominal Working Pressure: 1500 PSI.

Aircraft Compatibility

The AN815-3D is a standard hardware component used in the plumbing systems of virtually all general aviation and many older transport/military aircraft that utilize 1500 PSI petroleum-based hydraulic, fuel, or oil systems. It is not specific to any one airframe but is a universal component specified by part number in countless maintenance and parts manuals.

Crucial Note: The correct fitting part number, size, and material for a specific application must be verified against the aircraft's Illustrated Parts Catalog (IPC) or maintenance manual.

Applications

• Joining two sections of 3/16" aluminum tubing in a straight run.

• Used in hydraulic systems utilizing MIL-PRF-5606 or MIL-PRF-83282 hydraulic fluids.

• Applicable for fuel, oil, coolant, and low-pressure pneumatic systems.

• Connecting rigid tubing to flexible hose assemblies via an intermediate fitting.

Why Choose AN815-3D?

Choosing a genuine, traceable AN815-3D fitting is a critical decision for flight safety. A leaking hydraulic or fuel line is a severe fire hazard. AN fittings are manufactured to exacting tolerances for the 37° sealing angle, thread geometry, material strength, and heat treatment. Using a non-certified or industrial fitting (such as a 45° flare JIC fitting) in an aviation application will result in a guaranteed leak and a dangerous condition. The "AN" marking and the blue anodized finish are the visual guarantees of a certified part that has been manufactured and tested to the highest standards of the aerospace industry.

The AN815-3D fitting creates a seal based on the principle of a metal-to-metal interference fit. The seal is not formed by the threads of the B-nut; their sole purpose is to provide the axial clamping force. This force is applied to the 37-degree flared end of the tube, pressing it against the 37-degree male conical seat of the AN815 union. The geometry of this connection concentrates the clamping force onto a very narrow, circular line of contact. The resulting compressive stress at this line is exceptionally high, exceeding the yield strength of the softer flared tube material. This causes a slight, localized plastic deformation of the flare, forcing it to perfectly conform to the hard, smooth surface of the fitting's cone. This intimate, 360-degree metal-to-metal contact creates a seal that is capable of containing fluid pressures of 1500 PSI and higher. The 37-degree angle is an engineered standard, chosen as an optimal balance that allows a durable flare to be formed on aluminum tubing without excessive work-hardening or cracking.

Note: This is a flight-critical fluid system component. The conical sealing surfaces must be protected from nicks, scratches, or any damage. The mating tube flare must be inspected for cracks, concentricity, and surface imperfections before installation. The B-nuts must be tightened to the correct torque value specified in standard maintenance practices (e.g., AC 43.13-1B) to prevent over-stressing the flare (which can cause it to crack) or under-tightening (which will cause a leak). Never use any form of thread sealant or tape on the sealing surfaces of flared fittings.

Documentation

The definitive technical requirements for this component are detailed in Army-Navy specification AN815 and its modern successor, SAE AS5175. These proprietary documents must be sourced directly from the relevant standards organizations for complete engineering specifications.