Chapter 19 - Chapter Nineteen Fasteners The Big Picture You...

629
C H A P T E R
N I N E T E E N
FASTENERS
The Big Picture
You Are the Designer
19–1 Objectives of This Chapter
19–2 Bolt Materials and Strength
19–3 Thread Designations and Stress Area
19–4 Clamping Load and Tightening of Bolted Joints
19–5 Externally Applied Force on a Bolted Joint
19–6 Thread Stripping Strength
19–7 Other Types of Fasteners and Accessories
19–8 Other Means of Fastening and Joining
Discussion Map
■
Fasteners connect or join two or more components. Common
types are bolts and screws such as those illustrated in
Figures 19–1 through 19–4.
THE BIG PICTURE
Fasteners
In this chapter, you will learn to analyze the performance of fasteners and to select suitable types and sizes.
Discover
Look for examples of bolts and screws. List how many types
you have found. For what functions were they being used?
What kinds of forces are the fasteners subjected to? What
materials are used for the fasteners?
A fastener is any device used to connect or join two
or more components. Literally hundreds of fastener
types and variations are available. The most common
are threaded fasteners referred to by many names,
among them bolts, screws, nuts, studs, lag screws, and
set screws.
A bolt is a threaded fastener designed to pass through
holes in the mating members and to be secured by tight-
ening a nut from the end opposite the head of the bolt.
See Figure 19–1(a), called a hex head bolt . Several other
types of bolts are shown in Figure 19–2.
( a ) ( b )
FIGURE 19–1
Comparison of a bolt with a screw
(Reference 9)
FIGURE 19–2
Bolt styles. See also the hex head bolt in Figure 19–1 (Reference 9)

630 PART THREE Design Details and Other Machine Elements
A screw is a threaded fastener designed to be inserted
through a hole in one member to be joined and into a
threaded hole in the mating member. See Figure 19–1(b).
The threaded hole may have been preformed, for exam-
ple, by tapping, or it may be formed by the screw itself as
it is forced into the material. Machine screws , also called
cap screws , are precision fasteners with straight-threaded
bodies that are turned into tapped holes (see Figure 19–3).
A popular type of machine screw is the socket head cap
screw. The usual configuration, shown in Figure 19–3(f),
has a cylindrical head with a recessed hex socket. Also
readily available are flat head styles for countersinking to
produce a flush surface, button head styles for a low pro-
file appearance, and shoulder screws providing a preci-
sion bearing surface for location or pivoting. See Internet
sites 9 and 11. Sheet-metal screws, lag screws, self-tapping
screws , and wood screws usually form their own threads.
Figure 19–4 shows a few styles.
Search for examples where the kinds of fasteners
illustrated in Figures 19–1 through 19–4 are used. How
many can you find? Make a list using the names for the
fasteners in the figures. Describe the application. What
function is the fastener performing? What kinds of forces
are exerted on each fastener during service? How large is
the fastener? Measure as many dimensions as you can.