Fasteners
Chapter 5
Fasteners Objectives
• Describe USC threaded-fastener measuring
system
• Describe metric threaded measuring system
• Identify grade markings of threaded fasteners
• List and describe common thread repair tools
Objectives
• Identify and explain purpose of common
nonthreaded fasteners
• Explain importance of wire gauge sizes
• Identify common types of electrical fasteners
Introduction
• Automotive components are held together with
fasteners
• Much of a technician’s time is spent removing
and installing fasteners
• There are two basic groups
– Threaded
– Non-threaded
Threaded Fasteners
• Most common type of fastener
– Use spiral threads to wedge parts together
• Fastener Sizing and Torquing
– Must be correct strength and size
– Must be replaced with like size and quality
– Never install a heavier sheer pin to “fix” a problem
Threaded Fasteners
• Screws
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–
–
–
One of the most common threaded fasteners
Fits into a threaded hole
Different designs to meet attaching needs
Some require a wrench to install, others can be
installed with screwdrivers
– Often classed by shape of head
Threaded Fasteners
• Bolts
– Use a nut instead of a threaded hole
– Usually goes through parts that don’t have
threads
– Most have hex-shaped head
– Two different types
• Standard
• Torque-to-yield
Threaded Fasteners
• Studs
– Fastener with no head and threads on both ends
• Nuts
– Used with bolts and studs
– Many different designs
– Can be specialized to specific applications
Torque-to-Yield Bolt Installation
• Follow all manufacturer instructions on torquing
the bolt
• Typically first two steps involve an actual ft.lbs
reading on a torque meter
Torque-to-Yield Bolt Installation
• Final step requires tightening the fastener a
specified number of degrees
• Greatly reduces effect of friction on torque
readings
Threaded Fasteners
• Washers
– Often used to distribute loads
– Prevent a nut from becoming loose
– Prevent damage to a machined surface
Washers
•
•
•
•
Flat
Spring Lock
External tooth lock
Internal tooth lock
Nuts
Threaded Fasteners
• U.S. (English) Thread Sizes
– Manufactured to Unified System specifications in
Fractions of an Inch
– Threads can be course or fine depending on the
number of threads per inch
– Bolt size is determined by shank diameter, bolt
length, and threads per inch
Bolt Identification (Cont’d)
Bolt Identification
• Diameter
– Measured across the threaded area
• Thread pitch (English system)
– The number of threads per inch
• Thread pitch (Metric system)
– The distance in millimeters between two adjacent
threads
Metric Size Bolt Identification
Example
• A metric size bolt that is identified as
6mm x 30mm x 1.25mm:
– Has a shank diameter of 6 millimeters.
– Is 30 millimeters long from the bottom of the head
to the end of the shank.
– Has a distance of 1.25 millimeters between its
threads.
Imperial Size Bolt Identification
Example
• An Imperial size bolt that is identified as 3/8" x
2" x 24:
– Has a shank diameter of 3/8 inch.
– Is 2 inches long from the bottom of the head to the
end of the shank.
– Has 24 threads per inch.
Threaded Fasteners
• Metric Thread Sizes
– Same basic measurements as U.S. (English) bolts
– Pitch number differentiates between fine and coarse
as opposed to NC or NF ratings
Measuring Devices (Cont’d)
• Screw pitch gauge / Thread pitch gauge
– Is used to determine thread pitch of a bolt or screw.
• Machinist’s rule
– Is usually used to measure items that don’t require
extremely close tolerances, such as bolt lengths
Bolt Grade Markings
• Customary (inch) bolts
– Identification marks correspond to bolt strength.
– Increasing numbers represent increasing strength.
• Metric bolts
– Identification class numbers correspond to bolt
strength.
– Increasing numbers represent increasing strength.
• Metric and SAE size wrenches are not
interchangeable.
Threaded Fasteners
• Hardness and Strength
– Strength is identified by grade markings on the bolt
head
– Standards are set by the Society of Automotive
Engineers (SAE)
– Tensile strength is amount of pressure the fastener
can take before it breaks
Grade Markings
Threaded Fasteners
• Fastener Torque
– Must be tightened to the correct amount
– Not enough torque causes fastener to loosen
– Too much leads to breakage
Torque Wrenches
Thread Repair Tools
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•
•
•
Tap and Die Set
Heilicoil
Thread Restorer and Chasers
Screw Extractor or EZ-Out (Brand Name)
Thread Repair Tools
• Tap and Die Sets
– Dies are used to make external threads
– Taper taps must extend through hole to work
properly
– Bottoming taps thread to bottom of hole
Thread Repair Tools
• Helicoils
– Threaded device threads into a hole and provides
internal threads for a bolt
– Must be used in conjunction with a properly sized
drill and tap
Heilicoil
Thread Repair Tools
• Thread Restorers and Chasers
– Restoring files are used to smooth and shape
damaged threads
– Thread chasers fit over the damaged thread like a
fastener
• Turned back and forth over damaged threads until
repaired
Thread Restorer files
TAP
Screw Extractor-EZ Out
Nonthreaded Fasteners
• Snap Rings
– Often used to hold parts in place on a shaft
– Made from high quality steel that retains its shape
– Snap rings can be internal or external
Electrical Wire
• Replacement wire must be at least as heavy as
the wire being repaired
• Always try to match wire color
• Use diagrams to pinpoint wire purpose before
repairing
Electrical Wire size
Wire Sizes
Wire Crimpers
Connectors
• Two types of connectors-Solder and solderless
• Soldering
– Best repair method for wires
– Adds little or no resistance to circuit
– Use only resin based solder in automotive circuits
Acid based solder can add resistance to circuit.
• Terminal Connectors
– Device fastened to end of wire, allowing connection
to a component
– Most are covered with an insulator
Connectors
• Molded and Shell Connectors
– Many different shapes and sizes
– Matched in color, shape, purpose to help prevent
crossing circuits
Wire Connectors
Connectors
• Butt Connectors
– Connects two wires together
– Quick and easy to install, but may add resistance
• Keys
Nonthreaded Fasteners
– Used to retain a part on a shaft
– Fits into a slot called a keyway
– Locks the two parts into position
Nonthreaded Fasteners
• Splines
– Long teeth are formed onto inside or outside of a
part
– Matching part has splines on opposite side
Nonthreaded Fasteners
• Rivets
– Used to hold parts together that are hardly ever
disassembled
– Made from soft materials
– Rivets are removed by a drill or chisel
• Then drive shaft out with a punch
Rivets
Summary
• Threads are measured and classified using
U.S. (English) or metric system
• Fasteners must be used as designed
• Nonthreaded fasteners are also common
• Electrical terminals and wiring must be
maintained