How to Identify MS Screws and Why They Are Needed

The NAS (National Aerospace Standards) has a specific method to identify screws, bolts and other fasteners that are used in aircraft. These standards must be met for the aircraft to be used for military or business purposes. Many people do not understand the difference between MS (Military Standard) screws and others, because they do not realize the different options available are required. For example, MS screws must be used in military aircraft and in a variety of ways. AN (Army-Navy) screws and bolts are the same.


Every fastener that adhersto NAS standards has a code that has a specification number, followed by many dashes, numbers and letters. All of those dashes and other information indicate the length and diameter of the shank and the material the fastener was made from. These fasteners differ from regular ones you can purchase at almost any store because they are made to be tough and last a long time. Those fasteners that do not have any markings are considered low strength. For example, the same screws you use to put together a wooden bench would be far different from those to put the aircraft together.


The materials used are shown on the fastener label by a dash or letters. The dash means the material was cadmium-plated alloy steel and if there are letters, it means it was a different material. For example, a “C” would mean that corrosion-resistant steel was used and “DD” would mean aluminum was used as a material to make the fastener.

If the fastener is a special purpose material, it will have the mark“SPEC,” which tells the user that the fastener has been treated with heat to make it more durable and strong. Sometimes fasteners will be colored with lacquer to determine that those fasteners must be inspected by exposure to a magnetic field, which is called magnetic particle inspection.

Why They’re Important

The main reason Fastener Dimensions MS Machine Screws are important is to be up to code and standards of all aircraft, whether military or not. Those that require the NAS standards must have those fasteners, but any aircraft can use them in order to have the safest and strongest materials possible.

NAS standards are there to ensure that airplanes are made to withstand air pressure, weather and other situations. There are many different standards available, including MS, AN and NAS.


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