What You Need To Know About NAS Bolts
When you are involved in aircraft manufacturing, it is vital to have a basic understanding of fasteners, appropriate applications, and the standards used to manufacture, test, and identify these parts. NAS bolts are one of the most commonly utilized fasteners in airframe and component construction, and are crucial in building a safe, strong, efficient aircraft.
In order to insure uniform standards of suitability for the intended purpose, strength, and reliability, the United States military and the Aerospace Industries Association, along with global cooperation, have developed and published standards for all components of aircraft assembly, including NAS bolts.
To understand these specifications, and their use in all manufacturing environments, you should know some history of the evolution of the standards utilized, have some basic knowledge of the testing and verification process, and understand how these fasteners are identified, along with their suitable applications.
Before the Second World War, there were some attempts at setting uniform standards for the manufacture, testing, and strength of fasteners and metals, but the big step came during the war. The United States Air Force and the Navy, wanting to insure the reliability and uniformity of materials and components, developed their own standards. These were consolidated to become the AN, for Air Force-Navy, eventually coming to be known as MS, which stands for military standards, or military specifications.
The AIA, Aerospace Industries Association, introduced standards known as NAS, or National Aerospace Standard. You need to be familiar with these abbreviations, AN, MS, and NAS, as they are the benchmarks for the proper selection and usage of bolts in the aerospace industry.
Suppliers whose fasteners conform to these standards are providing very precise bolts, engineered and designed specifically for your heightened requirements.
Fasteners used in the aerospace industry are engineered for specific stresses, tolerances, environments, function, and location in or on the airframe structure. Take off, landing, and flight procedures generate extreme torsional, sheer, and other stress factors, not present in other machinery.
In addition, the nature of flight requires a high level of reliability. The aircraft and its systems must continue to function properly until the craft has landed.
Testing and Verification
Fasteners sold without these ratings are manufactured using a low carbon steel, bending and corroding easily, and may have a tensile strength of only 50,000-60,000 pounds per square inch (psi). Alternately, NAS bolts feature up to 160,000+ psi tensile strength, and are manufactured from corrosive resistant, heat-hardened steel.
Testing procedures ensure uniformity, and compliance to NAS standards. Bolts are inspected by magnetic, fluorescent, or other methods, and are often designated verified by markings on the bolt head, or colored lacquer.
Identification and Application
Bolts are divided into three major parts, the head, the grip, and the threads. Bolt heads are marked, or stamped, with various letters, numbers, and symbols to identify its type, size, material, etc.
NAS bolts have a cupped out head, and if designed for close tolerances, a raised or recessed triangle marking. Close tolerance bolts are used in close fit situations, and are machined according to much tighter specifications.
NAS bolts are utilized where high strength and durability is required. The National Standards Association in Washington, D. C. can provide you with more information on the identification system for fasteners, including NAS bolts. The Airframe Mechanics General Handbook is also a great reference for decoding the various markings used in identifying fastener hardware.
Understanding the development of a superior fastener, manufactured according to universal, rigid standards for uniformity, design, and functionality, can assist your production process, and help you identify the best supplier of NAS bolts for your company.
Photo Credit: Sean MacEntee via Flickr