NAS1611-106 – Aerospace Preformed O-Ring
Part Number: NAS1611-106
Manufacturer: National Aerospace Standard (AIA/NAS)
Military Specification: NAS1611 (Dash size -106)
Material Class: Ethylene Propylene (EPDM)
Overview Section
The NAS1611-106 is a precision aerospace-grade packing O-ring engineered for high-performance sealing in aircraft fluid systems. It is part of the NAS1611 series, which is the industry standard for systems utilizing Phosphate Ester hydraulic fluids (most notably Skydrol).
The "-106" dash size refers to its specific dimensional profile within the 100-series (standard 0.103" cross-section). Because it is composed of Ethylene Propylene, it is a specialized component required for commercial and business jet hydraulic systems, where standard Nitrile or Viton seals would suffer from rapid chemical degradation and failure.
Enhanced Technical Data
| Technical Metric | Specification Data |
| Inside Diameter (ID) | 0.174 in (4.42 mm) |
| Cross-Section (W) | 0.103 in (2.62 mm) |
| Outside Diameter (OD) | 0.380 in (9.66 mm) |
| Material Base | Ethylene Propylene (EPDM / NAS1613 Class 1) |
| Durometer (Hardness) | 80 Shore A (Nominal) |
| Operating Temperature | $-65°F$ to $+250°F$ ($-54°C$ to $+121°C$) |
| Fluid Compatibility | Phosphate Ester (Skydrol), Water, Steam |
| Dash Size Series | 100 Series |
Advanced Engineering & Structural Application
The NAS1611-106 is engineered for Skydrol Compatibility and Thermal Stability. Phosphate ester fluids are notoriously aggressive toward common elastomers, requiring the specific NAS1613-compliant EPDM compound used in this seal.
Engineering Insight: The 100-Series Configuration
The 100-series O-ring profile is one of the most common in aerospace manifolds and valve bodies. The 0.103" cross-section provides a robust seal that balances "squeeze" (the compression required for a leak-proof joint) with "friction" (allowing for smooth movement in dynamic valve applications). The 80 Shore A hardness is specifically chosen to provide resistance to extrusion—preventing the O-ring from being squeezed into the clearance gaps between metal parts under high hydraulic pressure.
Sealing Reliability
Unlike commercial EPDM, the NAS1611-106 undergoes strict batch testing to ensure zero "voids" or surface imperfections. In a pressurized airframe, even a microscopic flaw in an O-ring this small can lead to a high-pressure mist leak, which poses both a fire hazard and a system failure risk.
Aircraft Compatibility
The NAS1611-106 is frequently found in the following systems:
Cessna Citation Series: Used in hydraulic control valves and landing gear selector modules.
Bombardier Challenger & Global: Extensively used in braking systems and environmental control system (ECS) valves.
Gulfstream: Found in various high-pressure Skydrol-based flight control manifolds.
Regional Jets (CRJ/ERJ): Standard hardware for primary hydraulic circuit maintenance.
The NAS1611-106 is a mission-critical seal for aircraft operating with advanced phosphate ester hydraulic systems. When maintaining high-pressure manifolds, using the correct NAS-standard hardware is the only way to ensure chemical compatibility and long-term airworthiness. This O-ring provides the necessary resistance to the harsh chemical environment of Skydrol while remaining pliable at the sub-zero temperatures encountered at cruising altitudes. Trust the precision of NAS1611-106 seals to protect your aircraft’s hydraulic actuators and valves from unscheduled maintenance and fluid loss.
Installation & Maintenance Addendum
Critical Chemical Warning: DO NOT use this O-ring in systems with mineral-based hydraulic fluid (MIL-H-5606) or fuel. Exposure to petroleum will cause the EPDM to swell and lose all structural integrity, resulting in immediate seal failure.
Lubrication: Use only Skydrol-compatible lubricants (such as Skydrol LD-4 or approved EPDM greases) during installation.
Visual Identification: These seals are usually solid black. Always verify the part number on the original hermetically sealed packaging to ensure you are not inadvertently installing a Nitrile seal into a Skydrol system.