CHAPTER 5 AIRCRAFT HARDWARE

CHAPTER 5 AIRCRAFT HARDWARE INTRODUCTION The importance of aircraft hardware is often overlooked because of the small size of most items. However, the safe and efficient operation of any aircraft depends upon the correct selection and use of aircraft hardware. This chapter discusses the various types of threaded fasteners, quick-release fasteners, rivets, electrical hardware, and other miscellaneous hardware. You must make sure that items of aircraft hardware remain tightly secured in the aircraft. Therefore, we will discuss proper safetying methods in this chapter. Aircraft hardware is identified for use by its specification number or trade name. Threaded fasteners and rivets are identified by Air Force-Navy (AN), National Aircraft Standard (NAS), and Military Standard (MS) numbers. Quick-release fasteners are identified by factory trade names and size designations. When aircraft hardware is ordered from supply, the specification numbers and the factory part numbers are changed into stock numbers (SN). This change is identified by using a part-number cross-reference index. Q5-1. How is aircraft hardware identified for use? THREADED FASTENERS LEARNING OBJECTIVE: Identify com- mon types of threaded fasteners and the methods used to properly install and safety them. In modern aircraft construction, thousands of rivets are used, but many parts require frequent dismantling or replacement. It is more practical for you to use some form of threaded fastener. Some joints require greater strength and rigidity than can be provided by riveting. We use various types of bolts, screws, and nuts to solve this problem. Bolts and screws are similar in that both have a head at one end and a screw thread at the other. However, there are several differences between them. The threaded end of a bolt is always relatively blunt. A screw may be either blunt or pointed. The threaded end of a bolt must be screwed into a nut. The threaded end of the screw may fit into a nut or directly into the material being secured. A bolt has a fairly short threaded section and a comparatively long grip length (the unthreaded part). A screw may have a longer threaded section and no clearly defined grip length. A bolt assembly is generally tightened by turning a nut. The bolt head may or may not be designed to be turned. A screw is always designed to be turned by its head. Another minor difference between a screw and a bolt is that a screw is usually made of lower strength materials. Threads on aircraft bolts and screws are of the American National Aircraft Standard type. This standard contains two series of threads—national coarse (NC) and national fine (NF). Most aircraft threads are of the NF series. Bolts and screws may have right- or left-hand threads. A right-hand thread advances into engagement when turned clockwise. A left-hand thread advances into engagement when turned counterclockwise. AIRCRAFT BOLTS Many types of bolts are used in modern aircraft, and each type is used to fasten something in place. Before discussing some of these types, it might be helpful if we list and explain some commonly used bolt terms. You should know the names of bolt parts and be aware of the bolt dimensions that must be considered in selecting a bolt. The three principal parts of a bolt are the head, grip, and threads, as shown in figure 5-1. Two of these parts might be well known to you, but perhaps grip is an unfamiliar term. The grip is the unthreaded part of the bolt shaft. It extends from the threads to the bottom of the bolt head. The head is the larger diameter of the bolt and may be one of many shapes or designs. 5-1