AN8-15 – Army-Navy Specification 1/2" Drilled Head Hex Bolt
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The AN8-15 is a high-strength, structural hex head bolt manufactured in strict accordance with Army-Navy (AN) aerospace standards. This is a foundational piece of aviation hardware, engineered for use in flight-critical joints subjected to significant shear and tension loads. With a shank diameter of 1/2 inch and an overall length of 1-5/8 inches, the AN8-15 is specified for use in countless applications across airframe, powerplant, and landing gear systems. The hexagonal head is drilled with provisions for safety wire, allowing for positive locking to prevent loosening under vibration—a mandatory safety feature for aviation.
Every aspect of the AN8-15, from its material composition and heat treatment to its thread manufacturing process, is tightly controlled by the AN specification. This ensures a level of strength, fatigue resistance, and reliability that commercial-grade hardware cannot provide. This fastener is not merely a bolt; it is a certified, traceable, and flight-critical structural component.
Key Features
Army-Navy (AN) Specification Certified: Guarantees that the bolt meets the stringent material, manufacturing, and quality control requirements for aerospace use.
High-Strength Alloy Steel: Forged from high-grade alloy steel (typically SAE 4140 or 8740) and heat-treated to achieve a minimum tensile strength of 125,000 PSI.
Rolled Threads for Superior Fatigue Resistance: Features UNF-3A threads that are cold-rolled, not cut, creating a continuous grain structure that dramatically increases resistance to fatigue failure from vibration and load cycling.
Drilled Head for Positive Locking: The head is drilled to accept safety wire (e.g., MS20995), providing a secure, verifiable method of preventing rotation and ensuring the integrity of the bolted joint.
Cadmium Plated for Corrosion Resistance: Coated with a sacrificial layer of cadmium per specification QQ-P-416, providing excellent corrosion protection in the harsh aviation environment.
Technical Specifications
Part Number: AN8-15
Component Type: Drilled Head Hex Bolt, Airframe
Governing Specification: AN8 (now may be referenced under NASM8)
Material: Heat-Treated Alloy Steel (e.g., SAE 4140 / 8740)
Finish: Cadmium Plated per QQ-P-416, Type II, Class 3.
Dimensions:
Shank Diameter: 1/2 inch (0.500 in)
Overall Length (from under head to end): 1-5/8 inches (1.625 in)
Threads: 1/2-20 UNF-3A
Grip Length (unthreaded portion): 25/32 inches (0.781 in)
Minimum Tensile Strength: 125,000 PSI
Head Marking: Marked with the AN standard marking, typically a cross or asterisk, for positive identification.
Aircraft Compatibility
The AN8-15 is a standard hardware component used across all categories of certified aircraft, including military, commercial transport, and general aviation. It is specified in any structural application where the engineering drawings call for a bolt with these precise material and dimensional characteristics.
Crucial Note: The correct bolt part number and, most importantly, the correct grip length for a specific application must be verified against the aircraft's Illustrated Parts Catalog (IPC) or maintenance manual.
Applications
The AN8-15 is designed for critical structural connections throughout the aircraft. Common applications include:
Engine Mounts and Accessory Installations
Landing Gear Trunnions and Strut Attachments
Flight Control Surface Hinge Fittings
Wing and Empennage Spar Attach Points
Primary Airframe Structural Assembly
Why Choose AN8-15?
Choosing a genuine, traceable AN8-15 bolt is a flight-critical decision. Commercial or industrial-grade bolts lack the mandatory material certifications, the superior fatigue life of rolled threads, the specified heat treatments, and the provisions for positive locking. The failure of a single structural bolt due to material defects or fatigue can have catastrophic consequences. The "AN" designation is the guarantee of quality, ensuring that the fastener has been manufactured, tested, and inspected to the highest standards of the aerospace industry, providing the strength and reliability required for safe flight.
The profound fatigue resistance of the AN8-15 bolt is a direct result of its mandatory rolled thread manufacturing process. Unlike machine-cut threads, which sever the material's grain structure and create microscopic stress risers at the thread root, rolled threads are formed by a cold-working process. A precision-ground bolt blank is forced between hardened steel dies that plastically deform the surface, causing the material to flow into the shape of the thread root and crest. This cold-working process induces a state of compressive residual stress at the critical thread root area and creates a continuous, unbroken grain flow that follows the contour of the thread. This compressed, smoothly contoured grain structure is exceptionally resistant to the initiation and propagation of fatigue cracks. As a result, a bolt with rolled threads can exhibit a fatigue life that is 50-75% greater than that of a geometrically identical bolt with cut threads, a non-negotiable engineering requirement for fasteners subjected to the constant vibration and cyclic loading inherent in aircraft operations.
Note: This is a flight-critical structural fastener. The grip length of the bolt must be carefully matched to the total thickness of the materials being joined. It must be installed with the correct mating nut (e.g., AN310 or AN365) and washer (e.g., AN960) and torqued to the value specified in the applicable aircraft maintenance manual (e.g., per AC 43.13-1B). After torquing, it must be positively secured with safety wire. Installation must be performed by a certified A&P mechanic.
Documentation
The definitive technical requirements for this component are detailed in Army-Navy specification AN8 and its modern successors (e.g., NASM8 / ASME B18.2.1). These proprietary documents must be sourced directly from the relevant standards organizations for complete engineering specifications.