Page 87 - Analysis and Design of Machine Elements

Detachable Joints and Fastening Methods
Many other types of threaded fastening methods are available in various applications, 65
for example anchor bolts to fix machines on the foundation, or eyebolts to lift machine
components and so on.
3.3.2 Threaded Fasteners
Threaded fasteners are standard and commercially available products used to connect
two or more elements. The possibility for different combinations of material grades,
thread dimensions, tolerance grade and manufacturing methods forms a large variety
of threaded fasteners. These combinations are considered in American National Stan-
dards, British Standards, Chinese Standards, ISO Standards and so on [6, 7]. The use of
standard products offers the advantages of interchangeability and low cost, and guaran-
tees they are indispensable devices throughout the industrialized world.
Threaded fasteners perform the function of locating, clamping, adjusting and trans-
mitting force from one machine element to another [5]. They form a big family, including
bolts, studs, machine screws, setscrews, nuts and so on. A bolt is a headed, threaded fas-
tener designed to connect two unthreaded components with the aid of a nut, as shown
in Figure 3.3a, b. Bolts have standard thread length and total length. Various standard
head styles and thread configurations are readily available. A stud is a headless fas-
tener threaded on both ends and is usually screwed permanently into a tapped hole
(Figure 3.3c).
A screw (machine screw or cap screw) is a headed, threaded fastener designed for the
assembly of two components, one of which contains its own internal thread as shown in

Figure 3.3d. Screws generally have several head (see Figure 3.4) and tip configurations,
and are tightened by a screwdriver into tapped holes.
Headless setscrews are designed to bear directly on the mating part by being inserted
into tapped holes to prevent relative motion (see Figure 3.3e). Figure 3.5 shows several
types of points of setscrew. The setscrew transmits torque by the friction between the
point and the mating part or by the resistance of the material in shear.
Different types of nuts and locknuts are available. The purpose of using nuts is to make
the threads deflect to distribute the load of bolt more evenly to the nut. The material of
nut must be selected carefully to match that of the bolt. Figure 3.3a–c shows common
hexagonal nuts. Jam nuts have reduced thickness and usually used together with hexag-
onal nuts for loosing prevention. Locknuts and lock washers are used for locating the
element axially on a shaft, as shown in Figure 10.8b.

(a)

(b) (c) (d) (e) (f)
Figure 3.4 Typical cap screw heads. (a) Slotted round-head screw. (b) Hex-head cap screw. (c) Phillips
round-head screw. (d) Hexagonal socket-head screw. (e) Slotted flat-head screw. (f) Slotted oval-head
screw.