What Are the Best MIL-SPEC Fasteners for Military Aircraft?

Fasteners are fundamental components in aviation engineering and construction, serving to securely join various parts of an aircraft. While the hardware and components regularly used in aviation settings are held to stringent performance and quality standards, those that are engineered for military purposes are subject to even stricter requirements as a result of the critical nature of defense missions. This is where military specification (MIL-SPEC) fasteners come in, such options being popularly used throughout defense applications as a result of their unique features, capabilities, and standardizations. In this blog, we will provide an overview of MIL-SPEC fasteners for those who wish to learn more, highlighting their significance and distinguishing features, as well as the most common types utilized in military aircraft.

What Are MIL-SPEC Fasteners?

MIL-SPEC fasteners are simply components that conform to the various military specifications established by the United States Department of Defense (DoD). While there are a number of standards for military-oriented fasteners, most follow the same standing goals and objectives, which are to guarantee interoperability among different military systems, ensure components are properly designed to withstand extreme environmental conditions, and maintain consistency in manufacturing and quality assurance processes.

MIL-SPEC fasteners can be categorized under various designations, with many being noted by particular prefixes in their part number. Generally speaking, the most recognized military specifications and prefixes one will come across include:

• Army-Navy (AN) Fasteners: These standards cover a broad range of hardware, including bolts, nuts, and screws that are designed for general military applications.
• Military Standard (MS): The MS prefix denotes that parts follow standards maintained by the DoD, with a wide array of military hardware components being included.
• National Aerospace Standard (NAS) Fasteners: While primarily developed for aerospace applications, NAS fasteners are known for their precision and high-strength characteristics, which benefits many defense-oriented objectives.

Each designation serves specific purposes, so the selection between each will often come down to the particular requirements of one’s project or applications.

Distinguishing MIL-SPEC Fasteners from Commercial Fasteners

While commercial aviation fasteners might look exactly like the MIL-SPEC fasteners found on a military jet, there are several key ways in which the two classes of parts differ. Manufacturing, quality assurance, and traceability requirements are where one will see the biggest differences, with an explanation being provided below.

• Rigorous Testing: MIL-SPEC fasteners undergo extensive testing to verify their mechanical properties and performance against expectations.
• Documentation: Comprehensive records are maintained for each fastener batch, detailing the manufacturing process, materials used, and testing results for reference.
• Traceability: Each MIL-SPEC fastener must be traceable back to its origin, ensuring accountability and facilitating quality control.

These stringent requirements ensure that fasteners for military aircraft perform reliably across flight conditions and stressors.

What Types of MIL-SPEC Fasteners Find Use on Military Aircraft?

Military aircraft utilize a wide range of fasteners to ensure the security of assemblies, with each specific category of hardware having a unique set of functions and applications. Here, we will share a brief introduction to the most popular parts for defense aviation.

Bolts

Bolts are a common form of fastener that generally comes in the form of a threaded shaft with a head on one side. When paired with a mating nut or internal threading element, bolts can secure anything from small assemblies to large structures with ample resistance against stressors.

Common Bolt Types:

• AN Bolts (ex. AN3 to AN20): Coming in the form of AN3, AN20, and other such standards, these bolts are commonly used across aircraft models to hold working pieces together.
• NAS Bolts: NAS bolts are often lauded for their high-strength design, which makes them critical for demanding aerospace applications.
• MS Bolts: Bolts conforming to military standards are often used for specialized applications, such hardware often meeting rigorous specifications.

Many MIL-SPEC bolts are referenced in technical manuals or recommended by manufacturers, so one should always take the time to determine which options are best for their operations.

Nuts

Nuts are often small hardware components with internal threading and external gripping surfaces, allowing them to be tightened to the end of bolts for establishing secure joints. The nuts used in military aviation often take advantage of advanced features or materials to ensure ease-of-use and reliability.

Common Nut Types:

• Self-Locking Nuts: With features that prevent loosening as a result of vibration, self-locking nuts are widely used within military aircraft.
• Hex Nuts: Hex nuts are fairly standard in design, featuring a hexagonal exterior that promotes optimal torque with each manual turn of a tightening tool.
• Barrel Nuts: When structures or assemblies have space constraints or limited ability to access all sides, barrel nuts serve as a good solution for blind installations.

The nuts used for military aircraft often conform to standards like MS21042 and NAS1291, both of which promote compatibility and performance.

Screws

While similar to bolts with external threading on their shaft and a head on one side, screws are able to create their own threading or utilize a pilot hole to secure components together without nuts. This makes them useful for assemblies where bolts are not as suitable, as screws still provide ample security and resistance.

Common Screw Types:

• Machine Screws: As a recognized type across applications, machine screws will often be found in military aircraft for securing numerous assemblies.
• Self-Tapping Screws: These screws create their own threads in materials, meaning a pilot hole is not needed.
• Socket Head Cap Screws: the design of socket head screws allows them to offer high strength for critical applications.

Military aircraft screws often adhere to standards like MS51957 and MS16995, those of which tend to specify material and dimensional requirements.

Rivets

As the final type we will discuss, rivets are permanent fasteners used to join sheets of material by having the headless side of their shaft deformed with a tool after insertion to secure assemblies.

Common Rivet Types:

• Solid Rivets: As the most basic option, solid rivets are known for providing strong, permanent joints for aircraft.
• Blind Rivets: Blind rivets are used when access to both sides of an assembly is limited.
• Flush Rivets: Flush rivets are often used in aerodynamic surfaces to reduce drag.

Military aircraft rivets often conform to standards like MS20426 and NAS1097, ensuring they meet necessary strength and durability requirements.

Where You Can Procure MIL-SPEC Fasteners for Military Aircraft

We at ASAP Semiconductor are proud to offer customers access to a wide range of high-quality MIL-SPEC fasteners designed specifically for military aircraft. Here, we offer access to thousands of top-quality parts that have been sourced from industry leaders across the globe, everything we carry being organized across curated catalogs and ready for purchase today. Take all the time you need to explore our offerings, knowing that our team is always just a call or email away from providing tailored support and hands-on service. We also feature online Request for Quote (RFQ) services with rapid turnaround times for completed submissions, so do not hesitate to get started.