AN3-11A - Aeronautical Standards Group​​ Undrilled Aerospace Bolt

AN3-11A – Aeronautical Standards Group Undrilled Aerospace Bolt

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The AN3-11A is a flight-critical, high-strength structural aerospace bolt manufactured in strict accordance with the Aeronautical Standard Group (AN) guidelines and MIL-DTL-6812 specifications. Featuring a 10-32 UNF-3A thread profile and a nominal shank diameter of 3/16 inches, this hex-head fastener is engineered for standard structural joints across airframe, control system, and power plant assemblies. The "A" suffix designates an undrilled shank and head configuration, making it the primary choice for applications utilizing self-locking prevailing-torque nuts (such as MS21042 or MS21044 series) where safety-wire holes or cotter pin paths are not required.

Fabricated from premium carbon or low-alloy steel—typically 8630, 8740, or 4130 chrome-molybdenum alloy—the AN3-11A undergoes rigorous heat treatment to achieve a minimum tensile strength of 125,000 psi ($861\text{ MPa}$). The bolt is finished with an electro-deposited zinc or cadmium plating (Type II Class 2 or equivalent) with a chromate treatment. This specialized plating serves as a sacrificial boundary layer, preventing galvanic corrosion when the fastener is driven into aluminum structural members. Featuring a precision-ground, unthreaded grip length of 11/16 inches, this bolt ensures that the high-shear forces within a structural joint rest entirely against the solid shank rather than the weaker threaded section.

The AN3-11A represents the foundational hardware standard for general aviation, commercial aircraft remediation, and military airframe upkeep. Its structural cross-section is precision-forged to eliminate internal stress concentrations and micro-voids, providing predictable fatigue life under alternating aerodynamic loads. For airframe mechanics, structural engineers, and fleet procurement managers, sourcing fully traceable AN3-11A hardware ensures that structural repairs conform completely to original type-certificate documentation, eliminating the risks of premature fastener shearing and joint relaxation.

Key Features

• High-Tensile Alloy Steel Matrix: Heat-treated to a minimum tensile strength of 125,000 psi, delivering superior safety margins for critical airframe structural tie-ins.

• Optimized Grip Length Protection: Features an unthreaded 11/16-inch shank area designed to bear primary shear loads, preventing thread-bearing deformation within the joint.

• Corrosion-Resistant Cadmium/Zinc Plating: Plated to maximize resistance to atmospheric oxidation and prevent galvanic corrosion when interfacing with dissimilar non-ferrous alloys.

• Undrilled Head and Shank Layout: Standard flat-hex head without safety-wire apertures, optimized for rapid torque installation paired with all-metal or nylon prevailing-torque locking nuts.

• Precision Rolled Threads: Thread profiles are rolled rather than cut after heat treatment, preserving material grain continuity and maximizing resistance to fatigue-crack propagation.

Technical Specifications

• Part Number: AN3-11A

• Component Type: Hex-Head Structural Aerospace Bolt

• Governing Specification: AN3 Standard / MIL-DTL-6812

• Thread Size / Pitch: 10-32 UNF-3A (Fine Thread)

• Nominal Shank Diameter: 3/16 Inch (0.1875 in)

• Grip Length (Unthreaded Portion): 11/16 Inch (0.6875 in)

• Total Length (Under Head to Tip): 1-1/64 Inches (1.0156 in)

• Head Configuration: Standard Hexagon Flat Head

• Width Across Flats (Wrench Size): 3/8 Inch

• Material Composition: Heat-Treated Medium Carbon / Low-Alloy Steel (e.g., 4130 / 8630 / 8740)

• Protective Finish: Cadmium Plated (QQ-P-416 Type II, Class 2 or equivalent) with Chromate Treatment

• Minimum Tensile Strength: 125,000 psi ($861\text{ MPa}$)

• Minimum Shear Strength: 75,000 psi ($517\text{ MPa}$)

• Certification Basis: Certificate of Conformance (CoC) / Full Traceability Documentation

Aircraft Compatibility

• General Aviation Fleet: Cessna 150/172/182/210 Series, Piper PA-28/PA-32/PA-34 Series, Beechcraft Bonanza/Baron Series.

• Commercial & Transport Airframes: Regional turboprops, utility transports, and light commercial platforms requiring standard structural hardware additions.

• Experimental & Light Sport Aircraft: Vans RV series, Kitfox, and specialized amateur-built aircraft.

• Note: Fastener selection, edge-margin limits, and installation authority must be verified strictly by referencing the target aircraft's structural repair manual (SRM), illustrated parts catalog (IPC), or approved standard hardware logs.

Applications

• Structural Airframe Joints: Securing primary skin panels, fuselage bulkheads, interior floor grid paths, and exterior fairing brackets.

• Flight Control Linkages: Providing the primary pivot bolts for non-rotating linkages, push-pull rods, and bellcrank bracket mounts.

• Engine Accessory Attachments: Mounting secondary fluid line brackets, cooling baffles, and electrical grounding straps within the engine cowl.

Why Choose AN3-11A?

Selecting a trace-certified AN3-11A structural bolt prevents the catastrophic joint failures associated with commercial-grade or non-aviation fasteners. Standard automotive or industrial grade-8 bolts lack the structural grain-flow uniformity, precise grip tolerances, and rigorous non-destructive testing (NDT) criteria mandatory for flight operations. Commercial fasteners driven into an aircraft joint frequently manifest inconsistent grip-to-thread ratios, causing the threaded plane to bear internal shear loads. This misapplication can induce rapid fatigue-crack propagation, thread stripping, and total structural joint failure under high-G aerodynamic maneuvers. AN3 series hardware ensures strict dimensional parallelism, providing predictable clamp loads and lasting shear capabilities throughout its lifetime.

The structural performance of the AN3-11A bolt depends on the mechanical principles of elastic clamping elongation and pure shear stress distribution across non-symmetric joint interfaces. When torque is applied during installation, the 10-32 UNF rolled threads engage the matching nut threads, converting rotational torque into a controlled linear tension vector along the bolt's longitudinal axis. This action stretches the bolt within its elastic deformation region, creating a permanent pre-load or clamp force that prevents joint separation under cyclic loading.

To withstand high-frequency aerodynamic vibration without inducing fatigue-crack propagation, the bolt features an isotropic granular grain flow created during the head-forging and thread-rolling processes. This continuous structural grain pattern eliminates the microscopic stress concentrations common to cut threads. The 11/16-inch unthreaded grip length is sized precisely to prevent the joint's mating shear planes from resting against the threaded region. Keeping the shear load on the solid shank capitalizes on the material's maximum cross-sectional area, avoiding the concentrated notch filters that trigger accelerated fatigue fractures and premature fastener failure under heavy flight dynamics.

Note: The AN3-11A is a structural, flight-governing fastener. Undersized grip applications, driving the threads into the joint's primary shear path, or over-torquing can deform the thread root, causing immediate loss of clamp load, fastener shearing, or structural joint failure. Fastener installation, stack-up washer configuration, and assembly inspection must be performed exclusively by a certified A&P/IA mechanic in strict compliance with the aircraft structural repair manual (SRM), standard practices manual, and FAA Advisory Circular AC 43.13-1B Chapter 7. Always verify that a minimum of one to three threads extend past the locking nut element and apply the exact dry or lubricated torque values specified for cadmium-plated hardware.

Documentation

• Aeronautical Standard Group AN3 Through AN20 Fastener Standard Blueprint Sheet

• FAA Advisory Circular AC 43.13-1B: Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair (Chapter 7: Aircraft Hardware)

• No public-facing standalone OEM engineering CAD model download is required for this open-source military standard component sequence; geometric parameters must be validated directly using standard global aviation hardware reference indices.

TECHNICAL FEATURES 

1. Hexagon Head
2. Undrilled Head
3. No Cotter Pin Hole
4. Fine Threads
5. UNF-3A
6. Material: Steel
7. Major Diameter: 0.19 in.
8. Thread Per Inch (TPI): 32
9. Length: 1.156 in.
10. Grip Length: 0.75 in.
11. Industry Standard Specification: AIA/NAS NASM3-20

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