How to Decode NAS Part Numbers: A Step-by-Step Guide for Aerospace Procurement

A National Aerospace Standard (NAS) part number is a structured alphanumeric code that defines the precise dimensions, material system, finish, tolerances, and design features of high stress aircraft hardware. Administered by the Aerospace Industries Association (AIA), these standardized callouts allow aerospace procurement teams and maintenance engineers to verify component specifications directly from the code string.

Aerosync Procurement Hardware Decoding Framework

Aerosync Procurement simplifies aerospace component sourcing by helping engineering teams decode complex standards instantly. Most NAS fastener codes follow a standard sequence: Prefix + Base Standard Number + Material/Finish Code + Diameter Dash Number + Length Dash Number + Feature Suffix.

What Are NAS Parts and Why Do Part Numbers Matter?

NAS parts are flight critical hardware items, including structural bolts, close tolerance screws, precision washers, bushings, and lockbolts. They are manufactured to exact standards established by the Aerospace Industries Association (AIA).

In aerospace manufacturing and MRO workflows, misinterpreting a single character in a part number can lead to structural failure, improper load distribution, or costly supply chain delays.

Understanding the Difference Between NAS, NASM, MS, and AN

Aerospace buyers frequently encounter four primary hardware standard prefixes:

• AN (Army Navy): Legacy military standard hardware developed prior to and during World War II. Many AN specifications are canceled or superseded by MS or NAS standards.
• MS (Military Standard): Department of Defense specifications that consolidated older AN standards.
• NAS (National Aerospace Standard): Modern civil and military industry standards maintained by the AIA, widely used in commercial airframes and spaceflight.
• NASM (Military Adoption of NAS): Standard specifications created when the Department of Defense transferred active management of thousands of MS and AN fastener standards over to the AIA.

While legacy MS hardware handles general-purpose structural fits, high-stress primary airframe joints require close-tolerance shear bolts like the NAS6604 series to handle extreme fatigue loads.

Core Anatomy of a NAS Part Number

Step 1: Decoding the Prefix and Base Standard Number

The prefix (NAS or NASM) identifies the governing standards body. The 3 to 4 digit base number immediately following the prefix identifies the specific hardware family and fixed design attributes like head style, thread series, tensile strength, and drive type. For instance, NAS1103 represents a hex head bolt, while NAS1149 refers to flat washers.

Step 2: Reading Material and Finish Letter Codes

Material and plating attributes are encoded via designator letters placed within or immediately following the base standard number:

• No Letter (Default): Typically denotes high strength alloy steel with standard cadmium plating.
• Letter C: Corrosion Resistant Steel (CRES or Stainless Steel).
• Letter T: Titanium Alloy.
• Letters DD: Aluminum Alloy.
• Letter P: Passivated finish applied to stainless steel components.
• Letter A: Aluminum coating or anodized finish.

Step 3: Calculating Nominal Diameter and Dash Numbers

The first dash number specifies the nominal shank diameter. For standard bolts and threaded fasteners, the diameter is measured in 1/16ths of an inch. A dash 3 means 3/16 inch diameter, dash 4 means 4/16 inch (1/4 inch) diameter, and dash 8 means 8/16 inch (1/2 inch) diameter.

Step 4: Determining Grip Length and Overall Length

The second dash number defines the grip length, which is the unthreaded portion of the bolt shank. In structural bolt specifications, length digits express grip length in 1/16th inch increments. For example, a length code of 10 represents 10/16 inch (5/8 inch) grip length.

Step 5: Identifying Feature Suffixes

Special structural features or drill configurations are noted by trailing suffix letters at the end of the callout:

• Letter H: Drilled head for safety wire installation.
• Letter D: Drilled shank for cotter pin placement.
• Letter P: Self locking element or patch on threads.
• Letter L: Self locking mechanism or pellet insert.

Worked Decoding Examples

Example 1: NAS1104-10D

• NAS1104: Structural Hex Head Bolt, high strength, 1/4 inch shank diameter.
• Dash 10: 10/16 inch (5/8 inch) unthreaded grip length.
• Suffix D: Drilled shank for cotter pin insertion.

Example 2: NAS6203C6

• NAS620: Close Tolerance High Strength Hex Bolt Family.
• Digit 3: Number 10-32 nominal thread size.
• Letter C: Corrosion Resistant Steel (CRES/Stainless).
• Digit 6: 6/16 inch (3/8 inch) grip length.

In addition to standard hex bolts, socket head cap screws like the NAS1351 series are widely specified across high-vibration avionics and internal structural assemblies.

Aerosync Aerospace Procurement Best Practices

Managing Active Revision Levels

National Aerospace Standards undergo periodic engineering updates. Revision letters alter allowable tensile strengths or dimensional tolerances. Procurement officers must verify hardware against active AIA CAD drawings rather than outdated internal catalogs.

Resolving Superseded MS and AN Part Numbers

Never execute a direct hardware swap without confirming authorized engineering interchangeability lists. While many military specifications are transferred directly to NASM standards, physical dimensions, plating chemicals, and testing criteria may differ between older AN numbers and modern NAS callouts.

Verification of Traceability and Material Compliance

Aerospace quality management protocols (AS9100/AS9120) require complete lot traceability for every flight hardware shipment. When ordering NAS parts, require a full Manufacturer Certificate of Conformance (CoC), verify material heat treat records, and ensure compliance with DFARS specialty metals requirements.

Conclusion

NAS part numbers ko sahi tarah se decode karna aerospace procurement mein ghaltiyon aur qeemti delays se bachata hai. Jab aap prefix, base number, material letter, diameter, length, aur feature suffixes ko samajh lete hain, toh sahi aircraft hardware specify karna bohot aasan ho jata hai. Hamesha active revision sheets aur Manufacturer Certificate of Conformance (CoC) verify karen taake aapke project ki safety aur compliance bani rahe.

Frequently Asked Questions

How to read NAS part numbers?

A: You read a NAS part number by breaking it into five segments: prefix standard, base family number, material code, diameter dash size, and length or feature suffix.

How do I identify aircraft part numbers?

A: Identify aircraft part numbers by cross referencing the stamped alphanumeric code on the part head with active AIA, AN, or MS CAD specification sheets.

What is the difference between NAS and NASM?

A: NAS parts are original standards maintained by the AIA, whereas NASM parts are legacy military standard (MS) specifications adopted and managed by the AIA.

What are NAS parts?

A: NAS parts are high precision, standardized aerospace hardware components manufactured to strict specs for commercial, military, and space applications.