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NAS1291-10 – High-Temperature All-Metal Self-Locking Hex Nut
Available now on the Airparts.aero Marketplace.
Overview
The NAS1291-10 is a National Aerospace Standard (NAS), high-temperature, all-metal, self-locking hexagon nut. This is a flight-critical fastener engineered to provide reliable, vibration-resistant locking action in environments that are too hot for a standard nylon insert lock nut. Its primary application is in the engine compartment, on firewalls, and near high-temperature systems like bleed air ducts and exhaust components. The NAS1291-10 part number specifically designates a #10-32 thread size nut made from cadmium-plated alloy steel, rated for service up to 450°F (232°C).
The locking mechanism is an integral, all-metal design. The top portion of the nut is precisely deformed into a non-circular shape. As a bolt is threaded through, it forces this section to elastically deflect, creating a powerful, spring-like frictional grip on the bolt threads. This "prevailing torque" is maintained even under extreme vibration and thermal cycling, ensuring the fastener remains secure. For any high-temperature bolted joint, the certified NAS1291 series nut is the definitive engineering solution for safe and reliable fastening.
Key Features
NAS Certified: Manufactured and tested in strict accordance with National Aerospace Standard NAS1291, guaranteeing material, dimensional, and performance integrity.
All-Metal Locking Design: The integral, deformed-thread locking mechanism contains no nylon or other non-metallic inserts, making it reliable at high temperatures.
450°F Service Rating: Certified for continuous service in high-temperature environments where a nylon insert nut (e.g., AN365/MS21044) would fail.
Cadmium Plated Alloy Steel: Fabricated from heat-treated, high-strength alloy steel and then cadmium plated for exceptional strength and corrosion resistance.
Prevailing Torque Mechanism: Provides a consistent locking force that is effective at any position on the bolt, independent of the clamp load.
Technical Specifications
Part Number / Specification: NAS1291-10
Component Type: Nut, Self-Locking, Hexagon, All-Metal
Thread Size (-10): #10-32 UNF-3B
Material: Heat-Treated Alloy Steel
Finish: Cadmium Plated, Type II (Yellow Chromate) per QQ-P-416.
Maximum Operating Temperature: 450°F (232°C)
Governing Specification: NAS1291 / NASM1291.
Aircraft Compatibility
Universal Aerospace Application: This is a standard high-temperature lock nut used throughout the entire aerospace industry on all classes of aircraft, from single-engine pistons to commercial airliners and military jets. It is used by all major manufacturers, including:
Textron Aviation (Cessna, Beechcraft), Boeing, Airbus, Bombardier, Piper, Gulfstream, and others.
Note: The correct nut for any application must be verified against the aircraft's specific Illustrated Parts Catalog (IPC) or maintenance manual, paying close attention to temperature requirements.
Applications
Firewall Forward: The primary application area. Used for mounting engine accessories, baffles, heat shields, fluid and electrical line clamps, and exhaust system supports.
High-Temperature Airframe: Used in areas near hot bleed air ducting for the environmental control and anti-ice systems.
Wheel & Brake Assemblies: Securing components in and around the brake assembly that are subjected to high radiant heat.
Why Choose NAS1291-10?
Using the correct temperature-rated hardware is a critical aspect of aviation safety. The most common maintenance error is to substitute a common, blue nylon insert lock nut (like an AN365) in a high-temperature application. The nylon insert in such a nut will melt and fail above 250°F, causing a complete loss of locking action. This will lead to the nut vibrating loose and the failure of the component it was securing, which can be catastrophic in an engine compartment. The NAS1291-10 is the specifically engineered, all-metal solution for this exact problem. Sourcing and installing a fully certified NAS1291 nut is a non-negotiable requirement for any bolted joint that operates above 250°F.
The locking principle of the NAS1291-10 is known as an elliptical offset lock, or "beam lock." During manufacturing, after the threads are fully formed, the top, castellated-looking portion of the nut is precisely crimped in two or more places. This action deforms the circular thread path into a slight ellipse. When the male fastener, with its perfectly circular thread profile, is threaded into this section, it acts as a mandrel. The bolt's threads must physically deflect the crimped segments of the nut outward, forcing the ellipse back into a circle. This elastic deformation creates a powerful, spring-like radial clamping force. This force generates the high, consistent frictional resistance—or prevailing torque—on the flanks of the bolt threads, which makes the nut highly resistant to loosening from vibration.
Note: The NAS1291-10 is a prevailing torque nut with a limited reusability. Per standard aviation maintenance practices, a nut should be discarded if its minimum prevailing torque falls below the value specified in the maintenance manual. It must not be used in applications where temperatures can exceed 450°F (232°C); for higher temperatures, a silver-plated A-286 CRES nut (like NAS1291C series) is required. Installation must be performed by a certified A&P mechanic.
Documentation
NAS1291: The National Aerospace Standard document defines all dimensional, material, and performance requirements for this series of nuts and is available through various standards providers.
