The Slide is about Bolts

1. Chapter 6
Fasteners

2. Objectives
• Identify the various fasteners used in vehicle
construction
• Remove and install bolts and nuts properly
• Explain when specific fasteners are used in
vehicle construction
• Explain bolt and nut torque values
• Summarize the use of chemical fasteners
• Identify hose clamps

3. Introduction
• Fasteners are the thousands of bolts, nuts,
screws, clips and adhesives that hold a vehicle
together
• Must be able to identify and use fasteners
properly
• Each fastener is engineered for a specific
application
• Always replace a fastener with exactly the same
type that was removed from the original
equipment manufacture (OEM) assembly

4. Bolts
• Bolt is a shaft with a head on one end and
threads on the other
• Cap screw is a high-strength bolt
• Bolts and cap screws are named after the body
part they hold
– Fender bolt, hood hinge bolt, etc.
• Also named after the shape and head drive
configuration

5. Bolts (continued)
• Bolt head is used to tighten the bolt
• Socket wrench fits over the bolt head
• Some metric/SAE sockets are very close in size
• Improper wrench or socket size could strip or
round off the both you are working on
– This could damage your tools or even cause an
injury if the tool slips off

6. Figure 6-1. Bolt measurements are needed when working.
Study each dimension of both USC and metric bolts

7. Bolts (continued)
• Bolt length is measured from the end of the
threads to the bottom of the bolt head
• Bolt length does not including the bolt head itself
• Bolt diameter, or bolt size, is measured around
the outside of the threads
• Bolt head size is the distance across the flats of
the bolt head
• Head size is given in fractions, like wrench size
– Common head sizes are 7/16, ½ and 9/16
– Common metric sizes are 8 mm, 10 mm, 13 mm

8. Bolts (continued)
• Both thread pitch is a measurement of thread
coarseness
• Bolts and nuts can have coarse, fine, and metric
threads
• Bolt threads are measured with a thread pitch
gauge
• Two common metric threads are coarse and fine
and can be identified by the letters SI and ISO
• Do not accidentally interchange thread types or
the bolt, or the part threads will be ruined

9. Bolts (continued)
• Bolts and nuts are available in right- and left-
hand threads
• Turn right-hand threads clockwise to tighten
• Turn left-hand threads counterclockwise to
tighten
• Left-hand threads have notches or a letter “L”
stamped on them

10. (A) Thread pitch gauge. The thread pitch gauge is fit against threads. Threads
that match the gauge equal the pitch number printed on the gauge.
Figure 6-3. Gauges can be used to tell thread, bolt or nut sizes.

11. Bolt Strengths or Grades
• Bolt strength is the amount of tightening force
that should be applied
• Bolts are made from different materials
– Have degrees of hardness for different situations
• Bolt grade markings are lines or numbers on top
of the head to identify hardness and strength
• Hardness or strength of metric bolts is indicated
by a property class indicator on bolt head

12. Bolt Strengths or Grades (continued)
• Bolt strength markings are given as lines, more
lines means more strength
• Metric bolt strength markings are numeric
– Higher number means more strength
• Tensile strength is the amount of pressure bolt
can withstand before breaking when pulled apart
• The harder the bolt, the greater tensile strength

13. Torque
• Torque is a measurement of the turning force
applied when tightening a fastener
• Over-tightening can stretch or break a bolt
• Under-tightening can allow bolt or nut to loosen
and fall out
• Torque specifications are tightening values for a
specific bolt or nut, given by the manufacturer

14. Torque (continued)
• Torque wrench measures torque values
• General bolt torque chart gives a general torque
value for the size and grade of bolt
• Bolt threads should be lubricated for accurate
results
– Refer to repair manual to see if threads should be
lubricated or dry
• Tightening sequence or torque pattern ensures
that parts secured by several bolts are clamped
down evenly

15. Figure 6-5. When tightening several bolts
that hold one part, a wheel, for example,
always use a crisscross pattern. This will
prevent part warpage and damage.

16. Torque (continued)
• Tighten fasteners in a crisscross pattern
• Tighten the fastener in steps, beginning at half-
torque then continue to ¾ torque, and then full
torque at least twice
• Be careful when tightening bolts and nuts with
air wrenches
– Easy to stretch or break a bolt in an instant
• Air wrench can spin the bolt or nut so fast that it
can hammer the fastener past its yield point,
stripping the threads or breaking the bolt

17. Nuts
• Nut uses internal threads and an odd shaped
head and is tightened onto a bolt
• Castellated or slotted nuts are grooved on top to
a safety wire or cotter pin can be installed into a
hole in the bolt
• Castellated nuts are used with the studs that
hold wheel bearings in position
• Self-locking nuts produce friction when threaded
onto a bolt; top of the nut can be crimped inward

18. Nuts (continued)
• Sometimes locking nuts must be replaced after
being removed
• Front wheel drive spindles sometimes use self-
locking nuts
• Jam nuts hold larger nuts in place
– Tightened against other nut to prevent loosening

19. Nuts (continued)
• Wing nuts have two arms for turning by hand
– Used when a part must be removed frequently for
service or maintenance, such as for air cleaners
• Acorn nuts are closed on one end for
appearance, to keep water/debris off the threads
• Body nut has a washer formed onto the nut to
distribute the clamping force of the thin body
panel or trim piece to prevent warpage

20. Figure 6-7. Body nuts are specially designed for specific holding applications.

21. Thread Repair
• Collision repair technician must frequently repair
damaged threads
• Tap is a tool for cutting inside threads in holes
• Die cuts threads on the outside of bolts or studs
• Special t-handles fit over tap or die for turning

22. Thread Repair (continued)
• Hold tool perfectly square to cut good threads
• Oil threads then rotate tap or die about one-half
turn
• Back it out about one-fourth of a turn
– Cleans out metal shavings and prevents tool
breakage
• Helicoil repairs badly damaged threads, and
allows the original bolt size to be used

23. Washers
• Washers prevent damage to surface of parts
and provide better holding power
• Flat washers prevent smaller bolt heads from
pulling through sheet metal and plastic
• Wave washers add a spring action to keep parts
from rattling and loosening
• Body or fender washers have large outside
diameter for the size hole in them
– Have better holding power on thin metal and
plastic parts
• Copper or brass washers prevent fluid leakage

24. Washers (continued)
• Spacer washers allow for the adjustment of parts
• Fiber washers prevent vibration or leakage but
cannot be tightened to a great extent
• Finishing washers have a curved shape for
appearance
• Split lock washers are used under nuts to
prevent loosening by vibration
• Shakeproof or teeth lock washers have teeth or
bent lugs that grip both the work and the nut

25. Screws
• Screws hold nonstructural parts on a vehicle
• Machine screws are threaded their full length
and are relatively weak
• Set screws have an internal drive head for an
Allen wrench and hold parts onto shafts
• Sheet metal screws and self-tapping screws
have pointed or tapered tips
• Trim screws have a washer attached
• Headlight aiming screws have a plastic adapter

26. Nonthreaded Fasteners
• Square keys, Woodruff keys prevent gears,
cams and pulleys from turning on their shafts
• Taper pins are used to locate and position
matching parts
• Dowel pins are used to position and align the
parts of an assembly
• Cotter pins prevent bolts and nuts from
loosening
• Snaprings hold parts onto shafts, and pop rivets
hold two pieces of sheet metal together

27. Figure 6-11. Keys and set screws are both used
to align parts on shafts. (A) Key and keyway.
(B) Set screw application

28. Hose Clamps
• Hose clamps hold radiator hoses
• Also hold heater hoses or other hoses into their
fittings

29. Adhesives
• Epoxy is a two part bonding agent that dries
harder than adhesive
– Does not shrink when hard and is waterproof and
heat-resistant at moderate temperatures
• Trim adhesive is used to install trim pieces onto
the body surface
• Trim adhesive dries to a pliable rubber-like
consistency and will bond plastics, metal, rubber
and other materials to painted surfaces

30. Summary
• Fasteners make up the thousands of bolts, nuts,
screws, clips, and adhesives that literally hold a
vehicle together
• Bolt strength indicates the amount of torque or
tightening force that should be applied
• Nonthreaded fasteners do not use threads
– Keys, snaprings, pins, clips, adhesives