0506-03-002-0118

FASTENERS

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Course Objectives

After completing Fasteners Course Module, the trainees will

realize different kinds of fasteners and their fastening methods, qualities and
classifications; attain knowledge on OEM supplied bolts and nuts and the
locking systems
realize the importance of torque tightening values, standard torque
specifications and classifications - know usage of other fasteners such as cap
screws, machine screws, set screws, snap rings and cotter pins etc.

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Content

Function of Fastener
Bolts, Screws & Studs
Fastener Grading & Measuring
Nut, Washer, Locking device and their Function
Conclusion

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Function of fasteners

Two metals can be joined together by four basic methods:

Welding (brazing or soldering)

Riveting
Interference fit or press-fit
Threaded fasteners (screw, hex bolts, and nuts)

The latter method is most advantageous because the two metals can be taken
apart without being damaged.

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What is fastener?

A fastener is a hardware device that mechanically joins two or more objects

together. In general, fasteners are used to create non-permanent joints

Common fasteners include screws, bolts, nuts and rivets.

The terms bolts and screws do not refer to specific types of fasteners, but rather
how they are used (i.e. the application). Thus the same fastener may be termed a
bolt or a screw.

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Bolts vs screws
Bolts are for the assembly of two unthreaded components, with the aid of a
nut.
Screws are used with components, at least one of which contains its own
internal thread, which even may be formed by the installation of the screw
itself. Many threaded fasteners can be described as either screws or bolts,
depending on how they are used.

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Bolted joint in vertical section Screw joint 6
 Stud

Studs are a hybrid between a bolt and a screw, since one end of the stud functions
as a screw while the other functions as a bolt.

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Metric bolt specification

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Bolts

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Metric specification

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Cap Screws
A cap screw is a type of fastener used for making mechanical connections between
mating objects, to ensure that they are held together securely.

Cap Screw Hex Key L Wrench

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Cylinder Head Bolts
The Role of Cylinder Head Bolts in the Engine

-When properly fastened to the cylinder head, the bolts apply a force called bolt
tightening force.
-This force helps seal off the combustion chamber, the passages that move coolant
and lubricant in and out of the engine, and the ambient air.

-Cylinder head bolts maintain bolt tightening force at all times in extreme operating
conditions.
-They can withstand temperatures encountered during cold starts or running engines,
and they can handle both negative and high positive pressures.

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Machine Screws

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Self-tapping screw
A self-tapping screw is a screw that can tap its own hole as it is driven into the
material.

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Set Screw
A set screw is a type of screw generally used to secure an object within or against
another object, normally not using a nut. The most common examples are securing
a pulley or gear to a shaft. Set screws are usually headless (also called blind),
meaning that the screw is fully threaded and has no head projecting past the major
diameter of the screw thread.

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Imperial Vs Metric wrench sizes
SAE MM

5/16” 8

3/8” 10

7/16” 11

1/2" 13

9/16” 14

5/8” 16

11/16” 17

3/4” 19

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10.9 bolt is Tensile Strength 1,000 MPa (145,000 psi), Yield Strength 900 MPa (90% of 1,000).
Same as grade 8 Customary Bolt.
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 Threads are measured by counting the number per inch.
Thread on metric threaded fasteners are measured by the
distance between threads (pitch) in millimeters.
Fig. Measuring Threads Per Inch (Top) and Pitch
(Bottom)

Using a Thread Gauge to Determine Threads Per Inch or Pitch.

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Nut, Washer, Locking device and Their function

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What is Nut?
A nut is a type of fastener with a threaded hole. Nuts are almost always used in
conjunction with a mating bolt to fasten multiple parts together. The two partners
are kept together by a combination of their threads' friction (with slight elastic
deformation), a slight stretching of the bolt, and compression of the parts to be
held together. Nuts are graded with strength ratings compatible with their
respective bolts; for example, an ISO property class 10.9 nut will be able to support
the bolt proof strength load of an ISO property class 10.9 bolt without stripping.
Likewise, an SAE class 5 nut can support the proof load of an SAE class 5 bolt, and
so on.

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Standard Nut Strength Markings
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Standard Nut Strength Markings
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Clamp force is not maintained
Threaded assemblies loosen because of:
A. Gaps: In order to make the assembly possible, nuts and bolts
must have some tolerance, which creates gaps between the
threads.
Parts tolerance

B. Vibration & side-to-side movement: These gaps allow the

parts to move from side-to-side when exposed to vibration.

Vibration and loosening

C. Expansion/contraction & loosening: Expansion and contraction
can also cause side-by-side movement. This, in addition to vibration,
leads to loosening and ultimately disassembly of parts.

Stretching of the bolt beyond its yield point and thermal

expansion/contraction of parts leads to lack of structural
rigidity and relaxation of parts
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In applications where vibration or rotation may work a nut loose, various locking mechanisms
may be employed: lock washers, jam nuts, specialist adhesive thread-locking fluid such as
Loctite, safety pins (split pins) or lock wire in conjunction with castellated nuts, nylon inserts
(nyloc nut), or slightly oval-shaped threads.

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Square Nuts
Square nuts, as well as bolt heads, were the first shape made and used to be the most common largely because they were much
easier to manufacture, especially by hand. While rare today due to the reasons stated below for the preference of hexagonal
nuts, they are occasionally used in some situations when a maximum amount of torque and grip is needed for a given size: the
greater length of each side allows a spanner to be applied with a larger surface area and more leverage at the nut.

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Hexagonal Nuts (Full Nut)
The most common shape today is hexagonal, for similar reasons as the bolt head: six sides give a good granularity of
angles for a tool to approach from (good in tight spots), but more (and smaller) corners would be vulnerable to
being rounded off.

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Wingnut
A wing nut or wing nut is a type of nut with two large metal "wings", one on each side, so it can be easily tightened and
loosened by hand without tools.

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Nylon nut (Nylon ring elastict stop nut, Self locking nut with nylon insert)
A nylon nut, also referred to as a nylon-insert lock nut, polymer-insert lock nut, or elastic stop nut, is a kind of locknut with a
nylon collar insert that resists turning.

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Flange Nut
A flange nut is a nut that has a wide flange at one end that acts as an integrated, non-spinning washer. This serves to distribute
the pressure of the nut over the part being secured, reducing the chance of damage to the part and making it less likely to loosen
as a result of an uneven fastening surface. These nuts are mostly hexagonal in shape and are made up of hardened steel and
often coated with zinc.

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Acorn nut (Dome Nut)(Crown Nut)
The acorn nut is a type of fastener which gets its name from its shape. Acorn nut is its common name and it is also called a crown
hex nut, blind nut, cap nut or domed cap nut. It is a nut that has a domed top to cover the threads. This is to prevent contact
with the external thread to protect the threads or protect other things the threads would rub against. In addition the dome gives
a more finished appearance. It is usually made of brass, steel, stainless steel (low carbon content) or nylon. It can also be chrome
plated and given a mirror finish.

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Castellated nut (Slotted Hex Nut, Castle Nut, Slotted Nut)
A castellated nut, sometimes referred to as a castle nut, is a nut with slots (notches) cut into one end. The name
comes from the nut’s resemblance to the crenellated parapet of a medieval castle.

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JAM NUTS (Lock Nut, Shear Nut, Low Hex Nut)

One way to lock a threaded part in place is with a jam nut. Usually a jam nut is thinner than a “full” nut, but otherwise
it is much the same as a full nut.

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Many different types of nuts are used on automobiles. Each type has a specific purpose.
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Washer
A washer is a thin plate (typically disk-shaped) with a hole (typically in the middle) that is normally used to distribute the load of
a threaded fastener, such as a screw or nut. Other uses are as a spacer, preload indicating device, locking device, and to reduce
vibration (rubber washer). Washers often have an outer diameter (OD) about twice their inner diameter (ID), but this can vary
quite widely.
Washers are usually metal or plastic. High-quality bolted joints require hardened steel washers to prevent the loss of pre-load
due to Brinelling after the torque is applied.

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Washers can be categorised into three types;
•Plain washers, which spread a load, and prevent damage to the surface being fixed, or provide some sort of insulation such as
electrical
•Spring washers, which have axial flexibility and are used to prevent fastening or loosening due to vibrations
•Locking washers, which prevent fastening or loosening by preventing unscrewing rotation of the fastening device; locking
washers are usually also spring washers.

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Plain washers
Plain flat washers are used to provide an even clamping load around the fastener. Flat washers are placed underneath a
nut to spread the load over a wide area and prevent gouging of the material. However, flat washers do not prevent a nut from
loosening.

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Lock Washers(Star washer, Shakeproof washer)
A lock washer is used under the nut and grips both the nut and the part surface. The three basic designs
are the internal, external, and the plain. . Tipped edges provide gripping power in the “off” direction.

External Internal External

Internal
When special holding power is required, a toothed lock washer is often used because it has many sharp, heat-treated
teeth to dig into the surfaces pressing against it.

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Helical Spring Washers (Split Washer, lock washer)
Frequently used method of keeping nuts and bolts tightly, especially when they are subject to machine vibration, is the
use of helical spring washers.

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Tab washer
A locking washer that works by having a side tab that can be bent into place against a nut. Metallic or non-metallic, the tab
washer notch prevents rotation relative to the shaft or fastener. Variations include single, multiple, formed and flat.

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Thread-locking fluid
Thread-locking fluid or threadlocker is a thin, single-component adhesive, applied to the threads of fasteners such as screws and
bolts to prevent loosening, leakage, and corrosion.

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Cotter Key or Pin
Cotter pins are used both with slotted and castle nuts as well as on clevis pins and
linkage ends. Use as thick a cotter pin as possible. Cut off the surplus length and bend
the ends as shown in Fig. If necessary, they may be bent around the sides of the nut.
Make certain that the bent ends will not interfere with some part.

Uses of cotter pin. A – Linkage. B – Clevis pin C – Slotted hex nut. D – Typical cotter pin.
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PINS
In their many forms, pins are convenient fasteners, utilized in many ways.

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Key

In mechanical engineering, a key is a machine element used to connect a rotating machine element to a shaft. The key prevents
relative rotation between the two parts and may enable torque transmission. For a key to function, the shaft and rotating
machine element must have a keyway and a keyseat, which is a slot and pocket in which the key fits. The whole system is called a
keyed joint. A keyed joint may allow relative axial movement between the parts.
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SNAP RINGS
Snap rings are used to position shafts, bearings, gears, and other similar parts. There are both internal and external
snap rings of numerous sizes and shapes. The snap ring must be expanded or contracted to be removed or installed.
Special snap ring pliers are used.

Be careful when installing or removing snap rings because overexpansion or contraction will distort and ruin them. If a
snap ring is sprung out shape-throw it away.

Snap Ring

Internal Prong Internal Hole Type

Type External Hole Type External “E” Type
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CLAMPS
Clamps compose a large family of useful fasteners, most of them are relatively simple and easy to use.

HOSE CLAMPS( Pipe Clip)

As their name implies, these clamps are used in many applications to secure hose ends to metal pipes. The important
thing about hose clamps is to get them tight when installed so they won’t leak fluid or air and won’t allow the hose
to work loose from the pipe due to slight relative motion or vibration.

Some of the Many Styles of Hose Clamps

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Reference
• Automotive Engines Theory and Servicing (James D. Halderman)
• Automotive Technology (Htun Myint Htay (M.E., Mechanical)
• EML2322L – Design & Manufacturing Laboratory Fasteners
• Thread locking (User’s Guide) Loctite
• MCDP Old Module(Fastener, Hand Tools and Measuring Tools)
• Fastener Basic (Bolt Depot.com)
• Types of Tap (HAND TAPS ISO 529)
• Htun Myint Htay (Facebook)
• Wikipedia
• Google

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