Use of safety wire

self-locking nuts-

Self-locking nuts provide tight connections that will not loosen under vibrations. Self-locking nuts approved for use on aircraft meet critical specifications as to strength, corrosion resistance, and heat-resistant temperatures. New self-locking nuts must be used each time components are installed in critical areas throughout the entire aircraft.Self-locking nuts are found on all flight, engine, and fuel control linkage and attachments. There are two general types of self-locking nuts. They are the all-metal nuts and the metal nuts with a nonmetallic insert to provide the locking action. The Boots aircraft nut and the Flexloc nut are examples of the all-metal type. See figure 5-7. The elastic stop and the nonmetallic insert lock nut are examples of the nonmetallic insert type. All-metal self-locking nuts are constructed either of two ways. The threads in the load-carrying portion of the nut that is out of phase with the threads in the locking portion is one way. The second way is with a saw-cut top portion with a pinched-in thread. The locking action of these types depends upon the resiliency of the metal.



Washers-

Finally, a hardware item that is simple. You are likely to encounter only a couple of different types of washers AN960 and AN970. The main purposes of a washer in aircraft installation are to provide a shim when needed, act as a smooth load bearing surface, and to adjust the position of castle nuts in relation to the drilled hole in a bolt. Also, remember that plain washers are used under a lockwasher to prevent damage to a surface.
AN960 washers are the most common. They are manufactured in a regular thickness and a thinner thickness (one half the thickness of regular). The dash number following the AN960 indicates the size bolt for which they are used. The system is different from others we have encountered. As an example, an AN960-616 is used with a 3/8" bolt. Yet another numbering system. If you see "L" after the dash number, that means it is a thin or "light" washer. An AN960C would be - yes, a stainless washer. I can tell you are getting more familiar with the system so I will throw another wrench into the equation - an AN970 washer has a totally different dash number system. I am not even going to tell you what it is. I will tell you that an AN970 is a larger area flat washer used mainly for wood applications. The wider surface area protects the wood.
There are other types of washers. I mentioned lockwashers that are made several different ways. They are often split ring, they are sometimes internal tooth and even external tooth (see Figure 5). You will also find nylon washers and finishing washers that usually have a countersunk head. So, as you can see, washers are not quite as confusing as other hardware even though we can make ft difficult if we wish.