AS3209-008 - Packing Preformed Fluorocarbon Rubber O-Ring 0.176 in ID 0.312 in OD 0.07 in Thick

AS3209-008 – Fluorocarbon (Viton®) Boss Seal O-Ring, 75 Durometer

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Overview

The AS3209-008 is a high-performance, preformed O-ring packing seal manufactured to the precise Aerospace Standard (AS3209). This O-ring is fabricated from a Fluorocarbon (FKM) elastomer, a material widely known by its DuPont trade name, Viton®, and is specifically engineered for creating a static seal on straight thread tube fittings and other port connections (bosses) in high-temperature environments. Its 75 durometer hardness provides an optimal balance of sealing force and material compliance for standard pressure applications.

The defining characteristic of this O-ring is its exceptional thermal stability, allowing it to maintain a reliable seal in continuous service temperatures up to 400°F (204°C). The AS568-008 size is designed for use with -4 (1/4 inch) tube fittings. This makes it the mandated sealing solution for common fluid connections in and around the engine compartment, firewall, and other high-temperature zones where a standard Nitrile (NBR) O-ring would rapidly degrade and fail.

Key Features

• High-Temperature Fluorocarbon (FKM): Fabricated from a Viton® or equivalent FKM elastomer, providing a continuous service temperature rating of up to 400°F (204°C).

• Designed for -4 Boss Seals: Specifically sized (AS568-008) for static axial sealing of -4 size straight thread tube fittings in their corresponding ports.

• Excellent Fluid Resistance: Offers superior chemical resistance to a wide range of petroleum-based and synthetic lubricating oils, hydraulic fluids, and jet fuels.

• 75 Durometer Hardness: The 75 Shore A hardness provides an excellent balance of sealing force and resistance to deformation for standard pressure applications.

• Aerospace Standard AS3209: Meets all dimensional, material, and quality requirements of AS3209, ensuring airworthiness and interchangeability.

• Material Identification: Typically brown in color to visually distinguish it from black Nitrile (NBR) O-rings, preventing incorrect installation.

Technical Specifications

• Part Number: AS3209-008

• Component Type: Preformed O-Ring Packing, Boss Seal

• Governing Specification: AS3209

• Material: Fluorocarbon Elastomer (FKM / Viton®)

• Hardness: 75 ± 5 Durometer Shore A

• Color (Typical): Brown

• Dimensions (AS568-008):

  • Inside Diameter (ID): 0.176 inches

  • Cross-Section (CS): 0.070 inches

• Typical Temperature Range: -15°F to +400°F (-26°C to +204°C)

Aircraft Compatibility

The AS3209-008 is a standard hardware component used across the entire aerospace industry in high-temperature fluid systems. It is not specific to one aircraft but is a fundamental component found on:

• Military Fighter, Transport, and Rotorcraft

• Commercial and Transport Category Airliners (Boeing, Airbus)

• Business and Corporate Jets (Textron Aviation, Bombardier, Gulfstream)

• High-Performance General Aviation Aircraft

Note: Verification of applicability is the responsibility of the installer. Always consult the current version of the aircraft or engine's Illustrated Parts Catalog (IPC) to confirm part number eligibility.

Applications

• Sealing of common -4 size (7/16-20 thread) straight thread tube fittings on firewall-forward components.

• Connections for fuel and oil pressure lines, instrument lines, and other low-flow fluid systems.

• Engine accessories, hydraulic pumps, and actuators in high-temperature zones.

• Any fluid system application where operating temperatures exceed the ~250°F limit of standard Nitrile (NBR) O-rings and an AS568-008 size is specified.

Why Choose AS3209-008?

The selection of the correct elastomer for the operating environment is a flight-critical decision. Substituting a standard black Nitrile (NBR) O-ring in a location specified for a brown Fluorocarbon (FKM) O-ring will result in the seal hardening, cracking, and failing from thermal degradation. This will cause a leak of hot, flammable fluid in a critical area of the aircraft. Using a certified AS3209-008 O-ring is the only way to guarantee you are installing the correct, high-temperature material required for a safe and airworthy repair.

The part number suffix "-008" is not an arbitrary number; it is a direct callout to the AS568 standard for O-ring sizes, which is the universal sizing chart for aerospace and industrial O-rings in the United States. This standard precisely defines the inside diameter (ID), the cross-section (CS), and their associated tolerances for hundreds of dash numbers. The AS3209 specification layers on top of this dimensional standard, dictating the material (Fluorocarbon), hardness (75 Durometer), and quality control requirements. This layered standards system is the foundation of aerospace hardware. It ensures that an AS3209-008 O-ring produced today by any qualified manufacturer is dimensionally identical to one produced 30 years ago, guaranteeing a perfect fit in any gland or boss that was originally engineered for that specific dash number. This interchangeability and strict configuration control are essential for the long-term maintenance and airworthiness of certified aircraft.

Note: This component has a finite shelf life defined by standards like ARP5316. The cure date must be verified prior to installation. It is a single-use part; a new O-ring must be used every time a fitting is reinstalled. The port and fitting sealing surfaces must be impeccably clean and free of scratches or damage. The O-ring must be lubricated with clean system fluid before installation.

Documentation

The base standard for this part is the Aerospace Standard AS3209. This is a controlled document managed by SAE International. OEM-specific application and installation data is contained within the aircraft's maintenance and parts manuals.