AN3H-13A – 10-32 x 1-3/8" Drilled Head Hex Bolt, Alloy Steel
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Overview
The AN3H-13A is a high-strength, drilled-head hex bolt manufactured to the rigorous Air Force-Navy (AN) standard. This fastener is specifically engineered for tension-loaded joints in high-vibration environments where a positive locking mechanism is mandatory. Its defining feature is the set of holes drilled through the flats of the hexagonal head, which are designed for the installation of safety wire (lockwire). With a 3/16-inch diameter and a 1-3/8-inch nominal length, this bolt is a staple for securing components and brackets throughout the airframe and powerplant.
It is important to note that while the informal callout "AN3-13 Drilled Head" is common, the precise part number for a hex head bolt of this specification is AN3H-13A, which denotes a hex head (H) and an undrilled shank (A). The standard AN3-13 part number technically refers to a clevis bolt with a drilled shank. This description is for the drilled-head hex bolt, AN3H-13A.
Key Features
Drilled Head for Lockwiring: The hexagonal head is cross-drilled to facilitate the installation of safety wire, creating a positive, anti-rotation locking mechanism that is visually verifiable.
High-Tensile Alloy Steel: Manufactured from heat-treated alloy steel (typically 4140 or 8740) to a minimum tensile strength of 125,000 PSI, providing exceptional strength for tension applications.
Cadmium Plating: Coated with a sacrificial cadmium layer per QQ-P-416 for superior corrosion resistance and consistent lubricity, ensuring accurate torque application.
Rolled Threads: Features #10-32 UNF-3A threads that are cold-rolled, not cut. This process significantly increases fatigue life by improving the grain structure at the critical thread roots.
Undrilled Shank: The "A" designation signifies a solid, un-drilled shank, for use with various types of nuts where the primary locking feature is the safety-wired head.
AN Standard Compliance: As a true AN-standard part, it guarantees interchangeability, dimensional accuracy, and material integrity for airworthy installations.
Technical Specifications
Part Number: AN3H-13A (Note: Commonly specified as AN3-13, Drilled Head)
Component Type: Drilled Head Hexagonal Bolt
Governing Specification: AN3H / NASM3H
Material: Alloy Steel (e.g., 4140, 8740), heat-treated
Minimum Tensile Strength: 125,000 PSI
Finish: Cadmium Plate per QQ-P-416, Type II, Class 2
Diameter: 3/16 inch (0.1875 inches)
Nominal Length (under head to end): 1-3/8 inches (1.375 inches)
Grip Length (Unthreaded Shank): 1 inch (1.000 inches)
Thread Specification: #10-32 UNF-3A
Aircraft Compatibility
The AN3H-13A is a standard hardware component, not specific to a single aircraft model. It is used ubiquitously across all segments of aviation where engineering drawings specify a 10-32 drilled head hex bolt of this length. Applications span:
Military Aircraft
Commercial and Transport Category Aircraft
General Aviation (Piston and Turbine)
Rotorcraft
Note: Verification of applicability is the responsibility of the installer. Always consult the current version of the applicable Illustrated Parts Catalog (IPC) or maintenance manual to confirm part number eligibility for a specific location.
Applications
Powerplant: Securing engine accessories, magnetos, vacuum pumps, engine baffles, and exhaust system brackets.
Airframe: Attaching structural brackets, inspection panels, and system components located in areas of high vibration.
Systems: Mounting hydraulic components, filter housings, and fluid line clamps.
Why Choose AN3H-13A?
In aviation, there is no substitute for certified hardware. An AN3H-13A bolt guarantees the specific material chemistry, heat treatment, and manufacturing processes essential for flight safety. The use of a commercial-grade or non-traceable bolt would introduce a catastrophic risk of failure due to lower tensile strength, poor fatigue life, and susceptibility to corrosion. This certified fastener, with its provision for positive locking, ensures the joint will remain secure under the most demanding operational conditions.
The AN3H-13A is defined not just by its material, but by its precise dimensional controls, particularly its #10-32 UNF-3A thread specification. The "3A" designation denotes the tolerance class for an external thread (A). Class 3 is the tightest tolerance class in the Unified National thread standard, reserved for applications where a close, precision fit is critical. This tight tolerance between the bolt's threads and the mating nut's Class 3B internal threads minimizes play and ensures a more uniform distribution of load across all engaged threads. In the high-cycle fatigue environment of an aircraft, this uniform load distribution is paramount. A looser Class 2 fit, common in commercial hardware, can cause the first engaged thread to carry a disproportionate amount of the load, creating a stress concentration that can lead to premature fatigue crack initiation and failure. The Class 3A fit of this AN bolt is a critical, engineered safety feature.
Note: This is a flight-critical hardware component. Installation must be performed by a certified mechanic. A calibrated torque wrench must be used to apply the correct torque value specified in the maintenance manual to achieve proper preload. Safety wire must be installed in accordance with standard practices (e.g., AC 43.13-1B), ensuring it is new, clean, properly tensioned, and twisted correctly, with the pigtail bent back to prevent injury.
Documentation
The specifications for this fastener are maintained under the National Aerospace Standards (NASM), which have superseded many of the original AN drawings. Publicly accessible summaries of these standards can often be found through standards organizations.