AN5-13A – Undrilled Aerospace Hex Head Bolt
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The AN5-13A is a high-strength, structural aerospace bolt manufactured in accordance with Army-Navy (AN) standards, specifically designed for applications requiring high shear strength and reliability. As a member of the venerable AN bolt family, the AN5-13A features a 5/16-24 UNF-3A fine thread and is categorized as "undrilled," meaning it lacks the safety wire holes in the head and the cotter pin hole in the shank, making it ideal for use with self-locking nuts in non-rotating joints.
Fabricated from high-carbon alloy steel, these bolts are the backbone of airframe structural assembly. The "A" suffix denotes the absence of a hole in the shank, a critical distinction for procurement specialists ensuring compatibility with prevailing torque locknuts. The AN5-13A is engineered to provide a precise grip length, ensuring that the threaded portion of the bolt does not extend into the shear planes of the joined materials—a fundamental principle in aerospace structural integrity. Whether used in engine mounts, control surface hinges, or primary fuselage junctions, the AN5-13A delivers the predictable mechanical properties required for certified aircraft maintenance.
Key Features
High-Strength Alloy Steel: Manufactured from heat-treated carbon steel (typically AISI 4037 or 8740) with a minimum tensile strength of 125,000 psi.
Cadmium Plated Finish: Coated with Type II, Class 2 Cadmium (QQ-P-416) for superior corrosion resistance and consistent torque-tension characteristics.
Precision-Cold Headed: The head is formed through cold-heading processes to ensure optimal grain flow, enhancing the bolt's fatigue life and resistance to head-to-shank failure.
Controlled Grip Length: Features a specific unthreaded shank (grip) of 0.938 inches, preventing "thread-bearing" in shear applications.
Standardized Hex Head: Designed for standard wrenching tools, providing a reliable interface for torque application in tight clearances.
Technical Specifications
Part Number: AN5-13A
Thread Size: 5/16-24 UNF-3A
Bolt Type: Hex Head, Undrilled (No shank hole, no head hole)
Manufacturer: Various FAA-PMA Approved Manufacturers
Material: 4037 or 8740 Alloy Steel
Finish: Cadmium Plate per QQ-P-416, Type II, Class 2 (Yellow Dichromate)
Total Length: 1.469 inches
Grip Length: 0.938 inches (15/16 in)
Tensile Strength: 125,000 psi minimum
Shear Strength: 75,000 psi minimum
Governing Specifications: AN5 through AN20 series standards
Aircraft Compatibility
Cessna 100/200/300/400 Series
Piper PA-28, PA-32, PA-34, PA-44
Beechcraft Bonanza, Baron, and King Air Series
Experimental and Amateur-Built Aircraft
Note: AN5-13A bolts are used universally across almost all GA and commercial airframes. Always consult the Illustrated Parts Catalog (IPC) for the specific application and torque requirements.
Applications
Structural Joinery: Ideal for airframe skins, ribs, and bulkheads where shear loads are predominant.
Engine Mounts: Used in conjunction with specialized washers and locknuts to secure powerplants to the cradle.
Landing Gear Components: Utilized in torque links and non-pivoting structural junctions.
Why Choose AN5-13A?
The integrity of an aircraft is only as strong as its fasteners. By choosing genuine AN5-13A bolts, you are ensuring that the hardware meets the rigorous metallurgical and dimensional standards established by the Department of Defense and the FAA. Non-certified or "industrial grade" hardware often lacks the controlled grain flow and heat-treatment consistency required to withstand the high-frequency vibration and cyclic loading inherent in flight. The AN5-13A provides peace of mind, ensuring that every bolt in your airframe contributes to a known, certified safety margin.
The mechanical superiority of the AN5-13A lies in its grain flow management and stress concentration mitigation. During the manufacturing process, the bolt undergoes cold-working, which aligns the metallic crystals along the longitudinal axis of the shank and follows the contour of the head. This results in an anisotropic structure that is significantly more resistant to fatigue than bolts machined from bar stock.
From an engineering perspective, the AN5-13A is designed primarily for shear-critical joints. The 0.938-inch grip length is calculated to ensure the shear plane (the interface between the two joined materials) rests entirely on the smooth, unthreaded portion of the shank. If threads were allowed to cross the shear plane, the effective cross-sectional area would be reduced by approximately 25%, leading to high local stress concentrations and potential notch-failure. Furthermore, the Cadmium plating acts as a "sacrificial anode," providing galvanic protection to the underlying steel while also acting as a dry-film lubricant to ensure accurate clamping force during torque application.
Note: The AN5-13A is a structural fastener. Never substitute an "A" (undrilled) bolt for a standard bolt if the application requires a cotter pin or safety wire. All fasteners must be torqued to the values specified in the Aircraft Maintenance Manual (AMM) or AC 43.13-1B. Reusing fasteners that have been subjected to over-torque or significant corrosion is strictly prohibited.