Understanding NAS, MS, and BAC Fastener Standards

Bolts, rivets, nuts, and a wide array of other fasteners are central to helping aircraft assemblies maintain structural integrity. Because of the challenging conditions and forces associated with flight, without strict oversight, even a simple fastener could cause a major failure. As such, aerospace fasteners are subject to carefully defined standards that govern their materials, dimensions, and performance, with some of the most recognized being NAS, MS, and BAC. This blog will explore what each of these standards covers and their distinct role in the aviation landscape, as well as what goes into confirming they meet such requirements.

National Aerospace Standards (NAS)

National Aerospace Standard fasteners fall under the jurisdiction of the Aerospace Industries Association (AIA), which maintains them through the National Aerospace Standards Committee (NASC). Established in 1938, NAS specifications now number in the thousands and apply to a wide variety of aerospace hardware. NAS standards are notable for their emphasis on precision, involving factors like tight dimensional tolerances, high tensile strengths, and carefully created threads that reduce stress concentrations. Because of their exacting nature, NAS fasteners are often more costly, but most aerospace applications depend on them to maximize safety margins.

Military Standards (MS)

Military Standards were introduced by the U.S. Department of Defense in the late 1950s and early 1960s as the formal successor to Army-Navy (AN) specifications. They are not exclusively designed for aircraft, instead serving to promote reliability and interchangeability with standardized dimensions, strength ratings, protective coatings, and fatigue resistance for fasteners used across military platforms. While the MS series was canceled in 1994, its legacy continues in various industries and legacy builds.

Boeing Aircraft Company (BAC) Standards

BAC standards are proprietary to the Boeing Aircraft Company, applying to any hardware used in its aircraft so it is directly compatible and meets certain safety expectations. While some aspects of BAC standards may overlap with industry-wide standards, they are written to reflect Boeing's proprietary engineering practices, safety margins, and quality control. To be approved under BAC, fasteners need to satisfy specific benchmarks for:

Surface Finishes and Coatings: Anodizing, cadmium plating, or primers are specified for compatibility with adjacent materials and prevention of galvanic corrosion.
Material Traceability: Full documentation of alloy composition, lot numbers, and heat-treatment history are mandated to maintain accountability across the supply chain.
Boeing-Specific Testing Protocols: BAC fasteners are often validated through internal fatigue, vibration, and durability tests that exceed standard industry requirements.

Validating Fasteners to Standards

No matter whether a fastener is intended to be designated under NAS, MS, or BAC specifications, it must pass rigorous qualification and acceptance testing before it can be approved to guarantee that it conforms both on paper and in practice. While procedures vary between standards, common validation methods include:

Dimensional Inspection: Fastener diameter, thread pitch, head geometry, and shank length are measured against exact tolerances, often down to thousandths of an inch.
Tensile and Shear Testing: Fasteners are subjected to axial loads to test their tensile strength and lateral shear strength.
Fatigue Testing: Repeated load cycles simulate the stresses of flight to check that fasteners will not fail prematurely under vibration or flexing.
Torque and Preload Checks: Bolts and screws in particular are tested to verify they generate the correct clamping force without stripping or fracturing.
Material Analysis: Verification through spectrometry or chemical testing ensures the alloy composition matches the specification.
Coating and Corrosion Resistance Testing: Cadmium plating, anodizing, or dry-film lubricants are checked to confirm if they withstand salt spray or chemical exposure requirements.
Environmental Validation: Some standards incorporate tests for high/low temperature endurance, humidity cycling, and long-term vibration resistance.

Documentation Requirements

Equally important to testing procedures is traceability. Every fastener approved under BAC, MS, NAS, or AS standards needs to be supported by extensive documentation, such as:

Certificates of Conformance (CoCs): CoCs verify that parts meet the exact specification called for in procurement contracts.
Material Test Reports (MTRs): MTRs detail the chemical composition and mechanical properties of the fastener’s raw material.
Process Certifications: These certifications validate that treatments like cadmium plating, anodizing, or heat treatment were performed according to set procedures.

These forms of compliance have a direct impact on regulatory approval. The Federal Aviation Administration (FAA), European Union Aviation Safety Agency (EASA), and the U.S. Department of Defense all require that only fully traceable, specification-compliant fasteners be used in their respective domains, as counterfeit or undocumented hardware creates significant pressing risks in any aircraft system.

Explore Various Aviation Fasteners on Hardware Domain

In all, each standard corresponds to different operational requirements and regulatory approvals. Understanding what BAC, MS, and NAS standards for fasteners respectively entail empowers aircraft maintenance teams to swiftly locate what they need for the application at hand. If you are seeking a dependable source of fasteners that meet these stringent benchmarks, having a procurement partner with a varied inventory is invaluable.

ASAP Semiconductor stands ready to fill that role with Hardware Domain, with this streamlined purchasing platform making it easy for customers to find fasteners and other aviation parts by many standardized designations. In addition to only presenting compliant parts from reputable manufacturers, we also pride ourselves on delivering competitive pricing, fast lead times, and exceptional service for every customer. To see how else we can ease the process of fulfillment, connect with our experts at your convenience.