Industrial Skills

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Industrial Skills

• Fasteners

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Fasteners are used in manufactured products for
several basic purposes

• They simplify manufacture.
• They simplify repairs.
• They provide safety.

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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?

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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.
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Screws A large and important family of
fasteners.
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.

• The most common types of screws are

• Sheet-metal screws

• Wood screws

• Machine screws

• Set screws

Use Categories
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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.

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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.

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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.

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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.

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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

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

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

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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.

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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.

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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
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• 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.

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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.

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Sizes and Descriptions

• 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.

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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.
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• 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.

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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.

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International Organization for Standardization(
ISO )

• Established standards for classifying metric
  bolts and screws.

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• 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.

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• 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.

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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).

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• Hex and Square Nuts
• The most common nuts, generally made of steel and
  are hexagonal or square in shape.

• Jam Nuts Used to lock a threaded part in place.
  
• Castellated and Slotted Nuts Secure a nut in
  place so it cant possibly come loose.
• Self-Locking Nuts Stay firmly in place even
  with constant vibration.
• Many other types of nuts available for special
  uses.

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• 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.

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• 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.