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
How is aircraft hardware identified for use?
mon types of threaded fasteners and the
methods used to properly install and safety
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
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
Threads on aircraft bolts and screws are of the
American National Aircraft Standard type. This
standard contains two series of threadsnational
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.
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.