What Types of Screws Are Commonly Used on Aircraft?
The construction of a typical aircraft is quite complex, requiring millions of parts to establish the entire assembly. For a Boeing 747, around six million parts are needed, half of which are solely made up of fasteners. Fasteners are crucial for any assembly, creating temporary or permanent joints to secure parts together. Aircraft fasteners come in many types, some of which are used for structures big and small. While screws are often an overlooked component of many assemblies, they are crucial for the construction of a typical aircraft. Depending on the area in question, many types of screws may be used, examples including the AN526 screw, the AN366 screw, the truss head screw, and many others. In this blog, we will discuss some of the most common types of screws that are found on typical aircraft assemblies, allowing you to better understand the role of each and their importance.
Across all sections of the aircraft, the two most widely used screws are the AN525 washer head type and the AN526 screw. Both of these fasteners feature protruding heads, and operators may choose between a slotted or Phillips head based on available tools and requirements. While Phillips head screws are regularly used for many applications, one will find that older aircraft models have slotted-head screws as they predated the invention of the Phillips head.
The AN525 screw in particular is a structural screw produced from heat-treated 2330 nickel steel, and cadmium plating ensures corrosion resistance for a long and reliable service life. Generally, aviation applications will call for the No. 8 and 10 size AN525 screw. Meanwhile, the AN526 screw is a nonstructural type that is produced from 1020 low-carbon steel. Since there is a low amount of carbon present in these fasteners, they are not able to undergo heat-treating. As a result, they should never be implemented for structural fastening, and instead should be relied on for securing the cowling, fairings, and other various parts.
Whenever a screw is used on an aircraft to secure an assembly, it is highly recommended to utilize a washer under the head for the means of protecting the surface of a component and any paint or finish it may have. Additionally, washers also help to further distribute force, increasing reliability and service lives. Typically, an AN90-10L steel washer is useful for size 10 screws, though a No. 10 fiber washer is applicable as well. For a standard No.10 screw, an AN365-1032 fiber lock nut will be needed to ensure the security of the installation so that loosening does not occur as a result of vibration or other forces. Additionally, an AN366 winged nut plate can also be used instead, requiring riveting for rapid installation and removal.
For nonstructural components that need to be secured on or within the aircraft, sheet metal screws are the most common option. Sheet metal screws will commonly feature a truss head, and they will also either have a Phillips or slotted head. Type A variations are those with a point located at the end of the thread, while Type B screws exhibit a flat bottom below the threading. For both options, a Tinnerman nut plate with the NAS395 code may be used for completing the assembly, and No. 6, 8, or 10 sizes may be used.
For the instrumentation located in the cockpit and other areas, it is important that a non-magnetic screw type is implemented to ensure ample performance and to prevent any issues. As such, brass screws such as the AN520B round-head screw are used. These types may come in sizes such as 6-32, 8-32, and 10-32 with a slotted or recessed Phillips head. To make the mounting of these screws as simple as possible, special nut plates should be used. It is important that the right size is used to accommodate the length of the screw.
Beyond such common examples, there are various other screws that one may use. For instance, the flush-head countersunk machine screw with the code AN510 may be present for various aircraft applications, and they feature an 82-degree angle between the taper. Similar to many other variations, flush-head countersunk machine screws may feature either a slotted head or a recessed head. Another example of a common screw that is not as widely used is the fillister-head type, that of which has a hole for safety wiring to pass through to ensure that the assembly remains well secured under various forces and vibration. These screws are produced under the code AN502, and they will generally be made from 2330 nickel steel that is heat treated before cadmium plating is added.
With any type of screw, it is crucial that one regularly inspects installations to ensure the health of assemblies. If screws are beginning to falter with corrosion, cracks, or other various issues, they should be replaced as soon as possible to prevent any hazard or breakdown. Always replace the screw in question with one of the same material and grade, or any alternative that is acceptable based on the assembly in question. While one screw may meet the same performance standards, if it is of a very dissimilar metal, you may run into various issues that can lead to increased damage on surfaces and assemblies. When it comes time to begin sourcing all the screws and aircraft fasteners that you need for your operations, there is no better purchasing platform than Accelerating RFQs.
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