Mil-Spec Fasteners

Nationwide Aerospace Parts Distributor

Sesco Industries is a nationwide aerospace parts distributor, which includes mil-spec fasteners. Are you looking for mil-spec fasteners for aerospace applications? Request a quote today.

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When you reach out, we can go over the parameters of these mil-spec fasteners with you and how they may align with your needs. We are one of the few manufacturers around making military set screws. Upon request, full certifications are provided at no charge. These certifications assure our customers to bid on our aerospace parts without hesitation. We are fully approved by the Defense Logistics Agency of Philadelphia, PA to be on the QSLM list.

What are Mil-Spec Fasteners?

Mil-spec fasteners is short for military specification fasteners. In general, mil-spec fasteners are hardware components, like bolts, screws, nuts, washers, and rivets. These components are manufactured and tested to meet rigorous standards set by the U.S. Department of Defense (DoD). These standards ensure the fasteners can perform reliably under extreme conditions, such as high stress, temperature, vibration, or corrosive environments.

Key Characteristics

• Standardized Specifications: These fasteners are governed by specifications like MIL-DTL, military standard, or national aerospace standard.
• Applications: The most common applications for mil-spec fasteners are in the aerospace industry and as military equipment, such as vehicles, aircraft, weapons. They are also used for some critical industrial or high-performance commercial applications.
• Material and Strength Requirements: Mil-spec fasteners are made from high-grade materials, like stainless steel, alloy steel, and titanium. These fasteners must meet specific tensile strength, hardness, and corrosion resistance standards in order to pass.
• Dimensional Precision: Tight tolerances for dimensions and thread forms to ensure interchangeability and reliability.
• Traceability and Certification: These fasteners often include full documentation, such as material certifications, lot traceability, and test reports. It is essential for defense and aerospace contracts.

In short, mil-spec fasteners are crucial components where failure is not an option. They are more expensive than your commercial-grade equivalents, but essential in mission-critical applications. Turn to Sesco Industries for reliable mil-spec fasteners.

4 Reasons Why Mil-Spec Fasteners Are Critical in Aerospace

The use of these fasteners is crucial in the aerospace industry. Here are four key reasons for why they are critical.

1. Interchangeability: Due to the ease of interchangeability, these fasteners maintain consistency across aircraft platforms.
2. Fatigue and Corrosion Resistance: This aspect is especially important in high-altitude and marine environments.
3. Weight Optimization: Many mil-spec fasteners are designed to be strong but lightweight.
4. Traceability: This is crucial for quality control and safety certifications, such as FAA and DoD.

Common Aerospace Applications Using Mil-Spec Fasteners

Mil-spec fasteners are used extensively in aerospace applications due to their precision, strength, and reliability under extreme conditions. Here is a breakdown of where and why they are used in aerospace systems.

Aircraft Structures

• Use with airframe assembly, such as fuselage, wings, and tail.
• Skin panel attachment.
• Bulkheads, ribs, and spars.

Engines and Propulsion Systems

• Exhaust components.
• Turbine casings.
• Engine mounts.
• Fasteners must endure high temperatures, vibration, and thermal expansion.

Landing Gear

• Use in high-load, high-stress areas.
• Requires fasteners with exceptional fatigue resistance.
• Often uses titanium bolts and shear pins to reduce weight and increase strength.

Control Surfaces and Actuation Systems

• Ailerons, elevators, rudders, flaps.
• Must allow for precise motion while withstanding aerodynamic forces.

Avionics and Electronic Bays

• Mounting of circuit boards, sensors, and control units.
• Requires EMI shielding, vibration resistance, and sometimes non-magnetic properties to operate.
• Stainless steel and cadmium-plated fasteners are often used.

Satellite and Spacecraft Structures

• Requires low outgassing, temperature stability, and mass efficiency.
• Materials like titanium or Inconel are preferred.

Fuel and Hydraulic Systems

• Must prevent leaks under pressure and thermal cycling.
• Fasteners used with sealing washers and O-ring grooves.

Common Types of MIL-SPEC Fasteners

Here are some common types of mil-spec fasteners.

Screws

MIL-spec socket set screws aid in securing panels, internal components, and subassemblies across air, land, and sea platforms. These screws are particularly valued where precise alignment or periodic disassembly is required. Flat head screws are a subtype often used in flush-mounted assemblies as to not interrupt aerodynamic surfaces on military aircraft and missiles. Additionally, pan and round head screws are typically found in interior enclosures, racks, and control housings where aerodynamics are not a factor.

Bolts

Bolts are used in more structurally demanding roles where high tensile and shear strength are required, such as engine mounts, rotor hubs, suspension systems, and armored vehicle frames. The ability of these mil-spec fasteners to withstand high mechanical loads and dynamic stress makes them essential in both mobile and stationary platforms.

Hex head bolts and countersunk bolts are commonly used in aircraft and ground vehicles to secure key load-bearing components, while also ensuring smooth surface contours or flush finishes. Additionally, socket head bolts are well-suited for tight spaces—such as within avionics enclosures or propulsion systems—where they enable high torque application without the need for wide external access.

Nuts

Nuts typically complement bolts by screwing on and fixing them in place. To bolster their basic mechanical abilities, many incorporate self-locking features to bolster their contribution under vibration and thermal changes. This is achieved through either elastic polymer inserts or all-metal mechanisms, with the latter being preferred near high-temperature assemblies like jet engines or exhaust systems.

Subtypes such as hexagonal nuts, wing nuts, and castellated nuts are designed to address specific needs related to torque, accessibility, and safety. Hexagonal nuts are preferred for their strength and ease of use with torque tools in tight assemblies. Wing nuts allow for quick, tool-free installation and removal, making them ideal for components requiring frequent adjustment or maintenance. Castellated nuts, often used with cotter pins, provide enhanced locking security in high-vibration environments.

Rivets

Rivets provide a permanent joining method for thin-sheet materials used in the airframes of tactical aircraft, unmanned aerial vehicles (UAVs), and satellite enclosures, where weight sensitivity and high strength are an important aspect. Mil-spec rivets are manufactured for vibration resistance and long-term stability, with two main categories being widely used across defense platforms: solid rivets and blind rivets. Solid rivets are best known for their exceptional shear and tensile strength, making them the preferred choice for primary structural joints. On the other hand, blind rivets are used when access is limited to one side of the assembly, such as inside fuselage compartments, wing spars, or enclosed avionics bays.

Pins

Pins are commonly used to ensure alignment, secure retention, and allow adjustability in components such as aircraft control linkages, landing gear joints, engine cowl latches, and other assemblies requiring regular maintenance or precise alignment. Their straightforward design accommodates both permanent and semi-permanent installations, depending on how they are integrated with other fasteners in the system.

Washers

Washers play a crucial role in preserving joint integrity and extending the service life of equipment across nearly all bolted connections. They help minimize surface fatigue and maintain alignment under conditions involving thermal cycling and mechanical shock. Flat washers—especially those conforming to MS15795 standards—are widely used to evenly distribute loads and prevent fastener heads or nuts from embedding into softer materials, such as the aluminum alloys commonly used in military aircraft and naval vessels. In contrast, lock washers are designed to resist loosening caused by vibration, making them vital in dynamic platforms like combat helicopters and armored personnel carriers.