Fasteners

1. Industrial Skills
Fasteners

2. Fasteners are used in manufactured
products for several basic purposes:
They simplify manufacture.
They simplify repairs.
They provide safety.

3. When selecting a fastener for a
particular use, consider these factors:
Strength: Will it hold the loads and pressures?
Security: Will it remain attached?
Cost: Realistic?
Installation: Appropriate for situation?
Skill: Is specialized training needed?
Equipment: Is specialized equipment needed and available?
Appearance: If the fastener shows, which kind looks best?

4. Nails – Most common method of fastening
one wooden member to another.
 Simplest & quickest.
 May not result in the
strongest of joints.
 Many different sizes
and various shapes
of heads, points &
shanks.
 Each type designed
for a particular
purpose.
 Drive nails at angles
slanting toward or
away from each other
to get best holding
power.
Nails are
designated
by “penny” size,
originally a term
which related to price
per hundred but now
signifies length. The symbol
for penny is the lowercase letter
“d”. Nail diameter increases with
length. Nails are now sold by the pound.

5. Screws – A large and important family of fasteners.
The most common types of screws are:
Sheet-metal screws
Machine screws Set screws
Wood screws
“Mechanical devices for fastening things together. Essentially a
cylindrical or conical piece of metal threaded evenly around its
outside surface with an advancing spiral ridge and commonly
having a slotted head: it penetrates only by being turned, as with a
screwdriver.”
Use Categories

6. Wood Screws
Serve much the same purpose as a nail, but:
Provide greater holding power than a nail.
Screws can be easily removed and replaced.
Screws are neater in appearance and offer more decorative
possibilities.
In addition to fastening pieces of wood together – the
most common use of wood screws would be to anchor
objects (hardware) to a wood surface.

7. Sheet-Metal Screws
Also called “Tapping Screws” or “Self-Threading Screws”.
Used to fasten light pieces of metal together or to attach covers,
panels and other light parts.
These screws have sharp threads that can cut their own grooves
into metal.
They come with “coarse” or “fine” threads and are usually case
hardened to cut threads and withstand hard twisting forces.
Distinguishable from wood screws in that they are threaded all
the way from the point to the head.

8. Machine Screws
Used for the assembly of metal parts and usually are driven
into “threaded” holes rather than drawn tight with nuts.
Like all screws, there are many head designs to choose from.
Machine screw threads are also designated by the number of
threads per inch, just like bolt threads:
A 6-32 machine screw has a #6 body diameter and 32 threads per
inch of length.
Most machine screws are fully threaded to the head.

9. Set Screws
Frequently used to hold a knob, collar, pulley or gear to
a rotating shaft.
There are a variety of “head” or “point” styles, each best
suited for its job.
Generally made of high-strength material and are heat
treated.
Not an especially strong type of fastening – depend on
friction and “shear” to hold parts together.

10. Once you have decided to use screws, in
addition to the use category, you must
consider four things before ordering.
Type of head
Material made of
The length
The diameter

11. The “type of head” should include both the
“shape” and the “style”.
Pan Head
Truss Head Hex Head
Flanged Hex Head
Screw Head “Shapes”Screw Head “Shapes”Screw Head “Styles”Screw Head “Styles”

12. The most common “material screws are
made of” is steel.
 If the fastener is exposed to the
“weather” – steel alone does not offer
much protection against the harmful
effects of corrosion.
 Coatings offer more protection.
Steel Blued
Zinc Coated
Chromium
Galvanized
Nickel
Silver Plate
Gold Plate
 Marine Applications
may require different
metals and/or materials.
Stainless Steel
Aluminum
Copper
Brass
Bronze
Synthetic Materials
(Plastic or Nylon)

13. The “length” of screws commonly range
from ¼ inch to 4 inches. Shorter or longer
lengths are generally special order items.
(Metric lengths are also available)

14. Screw diameters can be expressed by the
“gauge” number or by the fraction of an
inch. (Metric diameters are expressed in mm)

15. American Screw Gauge
 Sizes are designated by length in inches
(millimeters).
 Diameters less than ¼ inch (6 mm) use gauge number.
 Diameters greater than ¼ inch use fractions of an inch.
 Wood screws are an exception to this rule in that they
generally go up to a #20 gauge (21/64”).

16. Bolts, Cap Screws, Nuts & Washers
Nomenclature of bolt-type fasteners tends to be confusing.
Bolts are usually used in plain holes drilled through the parts being
fastened.
Bolts are generally held in place with a mating nut.
When the nut for any bolt is turned down on wood, always use a flat
washer under the nut.
Cap screws are normally used in threaded holes, without a nut.

17. Machine Bolts/Cap Screws
Machine bolts have square or hexagonal heads.
Installed with a wrench.
Usually used if the parts to be joined are made of metal.
Cap screws generally look just like a machine bolt.
Slightly different application.
Screwed into threaded holes rather than being used with a nut.

18. Round-Head Bolts
Commonly used to fasten wood parts.
Most have a square neck under the head.
 Also used to fasten steel parts with square
punched holes.
A Carriage Bolt is the most common type of
round-headed bolt to be used when working with
wood.
A Plow Bolt has a flat, tapered head that fits into
a countersunk hole – primarily used with metal parts.
Used in the marine industry for attaching
cutters and other parts to dredges.
Plow Bolt
Carriage Bolts

19. Stove Bolts are available with the same types of
head designs as wood screws, in diameters from
5/32” to 1/2” and in lengths from 3/8” to 6 inches.
Studs are another type of threaded fastener, which have no
head at all and is merely a steel rod with threads on both ends.
One end is screwed into a part, other parts are
assembled over the studs and screwed in place with a nut.

20. Other “ Bolts”
Some fasteners are referred to as bolts
but are actually screws.
A Lag Bolt is really a “heavy-duty screw”
with a square or hex head.
Designed to be driven with a wrench.
Available in lengths from 1” to 6” and diameters
from 1/4” to 1/2”.
A Hanger Bolt is a fastener that has wood screw style
threads on one end and machine threads on the other.
No head on this type of “bolt”.
Designed to be a hidden fastener.

21. Threads – External helical ribs on the body of a bolt at the end opposite
the head.
The diameter of a bolt is determined by the diameter of the crest of the
threads.
The length of most bolts (or machine screws) is determined by the
measuring from the bottom of the head to the end of the threads.
Flat head bolts are measured from the threaded end to the top of the head.
The Head Size determines what size wrench or socket must be used to
turn or hold the bolt or nut.
A square or hexagonal bolt head is measured across the “flats”.
Example – A ¾” wrench is needed to turn a ½” diameter bolt head.
Sizes and Descriptions

22. Threads
Threads – External helical ribs on the body of a bolt. Usually a
bolt “mates” with internal threads of a nut.
The top of the rib is called the crest, or thread tip.
Bottom of the groove is called the thread root.
Threads are measured by counting the number per inch. (Metric
threads are measured by the distance between threads – pitch – in mm)
Thread gauges are available that match
threads against those on the gauge.

23. The type of threads that are used for most applications are
coarse with deep grooves.
Some threads are finer, with shallower grooves.
Bolts with fine threads are used only under special conditions – such
as when the parts being fastened have thin walls.
Bolts and screws normally have right-hand threads.
Turned to the right (clockwise) when tightened.
Occasionally, bolts, screws and nuts with left-hand threads
are needed.
Turned to the left (counter-clockwise) when tightened.

24. American National Standards Institute
( ANSI )
There are carefully controlled standards for threading
bolts and nuts.
ANSI establishes such things as the angle of threads,
the depth of the root and the manufacturing
tolerances (fit) which are referred to as the “Unified
Screw Thread Standards”.

25. International Organization for Standardization
( ISO )
Established standards for classifying metric bolts and
screws.

26. Grades and Head Markings – Inch-Series
The kind of steel bolts and screws are made of and the
treatment they receive during manufacture determine their
strength.
The Society of Automotive Engineers (SAE) has
established standards for classifying inch-series bolts and
screws into grades, based on their tensile strength.
Markings consist of radial “slashes”.
High-quality inch-series bolts and screws ¼” and larger have
them.
Grade 5 or better hardware should be used in most situations.

28. Grades and Head Markings - Metric
The kind of steel bolts and screws are made of and the
treatment they receive during manufacture determine their
strength.
The International Organization for Standardization (ISO)
has established standards for classifying metric bolts and
screws into property classes based on strength.
Numbers on the head indicate property class.
High-quality metric bolts and screws 4mm and larger have them.
Class 8.8 or better hardware should be used in most situations.

30. Nuts and Washers
Nuts have coarse or fine internal threads that correspond to
the threads of a bolt and are designed to “screw” onto the bolt
to fasten it in place.
A great variety of shapes and sizes for standard and special
applications.
Threads per inch or distance between threads can be determined
with a thread gauge just like bolt threads.
Nuts have three important dimensions:
Thickness
Distance across the flats
Inside diameter (same as that of the bolt with which it is to be used).

31. Jam Nuts – Used to lock a threaded part in place.
Castellated and Slotted Nuts – Secure a nut in place so it
can’t possibly come loose.
Self-Locking Nuts – Stay firmly in place even with constant
vibration.
Many other types of nuts available for special uses.
Hex and Square Nuts
The most common
nuts, generally made of
steel and are hexagonal
or square in shape.

32. A plain washer is simply a steel disk with a hole
through the center.
Like bolts and nuts the may be manufactured with a
variety of different materials
They help distribute the load over an area larger than
the head of the bolt or nut, thus reducing the stresses
that would otherwise exist.
Plain washers are identified by their outside diameter
and the diameter of the hole, which is the bolt size
rather than the actual diameter of the hole.
The washer thickness varies with the size of the
washer.

33. Lock washers are frequently used to keep nuts and
bolts tight, especially when they are subject to
vibration.
Helical Spring Washers – Made of tough spring steel.
They are split and one end of the split is bent up. When
the nut is tightened, the section of the washer that is bent
up “bites” into the nut and the fastened part.
Toothed Lock Washers – Has many sharp, heat-
treated teeth to dig into the surfaces pressing against it.
Many other types of washers are available for special
uses.