
Semi-permanent joining applications refer to methods used
to join different objects together, securely but not
necessarily permanently.

There are numerous ways of joining engineering materials
together, but we will deal with only the following:
• Bolts and nuts
• studs
• locking devices
• rivets, split pins and keys.
A
bolt is the term for a threaded fastener,
with a head, designed to be used with a nut.
 Several hundred different types of bolts are
used in engineering applications.
 Bolts can use various head shapes; hexagonal,
square, round, countersink or recessed.
 Machine screws normally have slotted heads,
but may have other drive configurations.
A
bolt or screw’s drive configuration will determine
what type of tool is used to fasten it.
 Each drive type is designed for a specific purpose and
has a special tool to drive it.
 Some of the more unusual ones, like the tri-wing®,
are used for tamper-proof applications, and are
difficult to remove without the correct tool.
 The
body of a bolt is divided into the thread and the
shank.
 The shank is the unthreaded part between the head
and the thread.
 The thread on a bolt or screw can be divided into
various categories; most bolts have only a partial
thread while machine screws usually have a full
thread.
 Bolts
are measured by the diameter and length of the
shank.
• For example, a bolt with a diameter of 14 mm and a length
of 60 mm is known as an M 14 x 60 bolt.
 Metric
bolts and screws are also classified according
to the type of thread.
 The standard types of thread are known as ISO metric
course or ISO metric fine.
 The head of any bolt is always in proportion to the
body diameter.
 Common threads are usually right-hand (bolt tightens
clockwise), but can also be left-hand.
 Research
five types of head styles.
 Sketch their profiles and state where they are
commonly used.
F
& M Pg. 95
 The
point style refers to the end of the thread.
 Different points on bolts or machine screws
are used for different purposes in engineering.
 Here are the five most common point styles:
 Mild
steel bolts either have a black appearance or are
coated with zinc for rust protection (galvanized
bolts).
 Some bolts and machine screws are also coated with
cadmium for rust protection.
 More expensive bolts are made from various grades
of stainless steel or brass for their superior anti-rust
properties.
A
stud is a fastener which is usually threaded at
both ends with an unthreaded shank in-between.
 One end is secured into a tapped hole and the
other is fastened with a nut.
• E.g. the manifolds are connected to the cylinder head of
an automobile engine.



Nuts are generally used in conjunction with bolts and
studs.
They are generally hexagonally shaped and available in a
wide variety of forms for specific engineering/production
purposes.
As can be seen below, the nut’s thickness and width
(across centres) is in proportion to the diameter of the
hole.
 We
use locking devices to prevent nuts from
wearing loose due to movement and
vibration. They can be divided into three
main groups:
• friction-locking devices,
• positive-locking devices and
• wiring.
These
consist of three main groups:
• lock nuts,
• stiff nuts (which resist coming loose)
• and special washers.
 Lock
nuts are used to lock up against an
ordinary nut to jam it against the bolt or stud.
They are slightly thinner than full nuts.
 Stiff
nuts have their own resistance to torque by
means of a nylon insert (nylock® nuts) or split head
like the Aero nuts. This prevents them from coming
loose as a result of vibration or movement.



Many different types of special washer are used as friction
locking devices. We will look at the spring washer and serrated
(or toothed) washer.
The diagram on the right illustrates one of
the more common types of spring (or lock)
washers used in engineering.
Serrated washers are designed for more specific purposes.
They are usually designed for specific bolt or screw head types
and nuts.
 These
devices tighten nuts very securely and
can be divided into four main categories:
• Slotted nuts
• Crown nuts
• Tab washers
• Lock plate
• Wiring
 These
nuts use a split pin to secure them in
the required position.
 These
are common used on the end of
automobile stub axles to retain the hub
assembly. A split pin us used to prevent the
nut loosening due to the rotation of the
wheel.
 Tab
washers have a smalltip which fits into a
recess next to the nut. Once the nut is
tightened, the sides of the washer are bent
up against the flats of the nut to prevent
unwanted nut rotation.
A
lock plate functions similar to a tab washer.
Once the nut is tightened , the lock plate is
inserted on either side of the flats of the nut
and screwed down to prevent any unwanted
rotation of the nut.
 These
points must be considered when
preparing single bolt joints:
• The appropriate diameter and strength must be
selected for the given purpose.
• The exact position of the hole is marked out and
punched with a centre punch.
• The punch mark makes drilling more precise because
it prevents the drill bit from wandering.
 You
should note the following:
• The joint face should lie across the plain shank of the
bolt, never across the threads.
• The bolt should pass through a hole of the correct
clearance.
• At least two threads should show beyond the nut when
tightened, to ensure full engagement.
• The bolt or machine screw should also be inserted in
such a way that it cannot fall out should the nut work
loose.
 The
flanges on a rolled steel joist (R.S.J, or Ibeam and T-beam) and channel bars are
slightly tapered.
 For this reason tapered washers are used to
keep the bolt’s head and the nut pulling truly.
 In the next section we will look at how several
bolts or rivets can be used to make very strong
joints.