Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw
www.TechnicalBooksPDF.comTools, Fasteners, and Safety 3Figure 1-5. Typical bolt (cap screw) grademarkings and approximate strength.The actual grade of bolts is two more than thenumber of lines on the bolt head. Metric boltshave a decimal number to indicate the grade.More lines or a higher grade number indicate astronger bolt. Higher grade bolts usually havethreads that are rolled rather than cut, which alsomakes them stronger. In some cases, nuts and machinescrews have similar grade markings.CAUTION: Never use hardware store (nongraded)bolts, studs, or nuts on any vehiclesteering, suspension, or brake component.Always use the exact size and grade of hardwarethat is specified and used by the vehiclemanufacturer.Figure 1-6. Every shop should have an assortmentof high-quality bolts and nuts to replace those damagedduring vehicle service procedures.NUTSMost nuts used on cap screws have the same hexsize as the cap screw head. Some inexpensive nutsuse a hex size larger than the cap screw head. Metricnuts are often marked with dimples to showtheir strength. More dimples indicate strongernuts. Some nuts and cap screws use interference fitthreads to keep them from accidentally loosening.This means that the shape of the nut is slightly distortedor that a section of the threads is deformed.Nuts can also be kept from loosening with a nylonwasher fastened in the nut or with a nylon patch orstrip on the threads. See Figure 1-7.
www.TechnicalBooksPDF.com4 Chapter Onesealers, such as Loctite, are used on thethreads where the nut or cap screw must beboth locked and sealed.Figure 1-7. Types of lock nuts. On the left, a nylonring; in the center, a distorted shape; and on the right,a castle for use with a cotter key.NOTE: Most of these “locking nuts” aregrouped together and are commonly referredto as prevailing torque nuts. This means thatthe nut will hold its tightness or torque andnot loosen with movement or vibration. Mostprevailing torque nuts should be replacedwhenever removed to ensure that the nut willnot loosen during service. Always followmanufacturer’s recommendations. AnaerobicWASHERSWashers are often used under cap screw headsand under nuts. Plain flat washers are used to providean even clamping load around the fastener.Lock washers are added to prevent accidentalloosening. In some accessories, the washers arelocked onto the nut to provide easy assembly.BASIC TOOL LISTHand tools are used to turn fasteners (bolts, nuts,and screws). The following is a list of hand toolsevery automotive technician should possess. Specialtytools are not included. See Figures 1-8through 1-26.Figure 1-8. Combination wrench. The openings are the same size at both ends. Noticethe angle of the open end to permit use in close spaces.Figure 1-9. Three different qualities of open-end wrenches. The cheap wrench on the leftis made from weaker steel and is thicker and less accurately machined than the standardin the center. The wrench on the right is of professional quality (and price).
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Tools, Fasteners, and Safety 3
Figure 1-5. Typical bolt (cap screw) grade
markings and approximate strength.
The actual grade of bolts is two more than the
number of lines on the bolt head. Metric bolts
have a decimal number to indicate the grade.
More lines or a higher grade number indicate a
stronger bolt. Higher grade bolts usually have
threads that are rolled rather than cut, which also
makes them stronger. In some cases, nuts and machine
screws have similar grade markings.
CAUTION: Never use hardware store (nongraded)
bolts, studs, or nuts on any vehicle
steering, suspension, or brake component.
Always use the exact size and grade of hardware
that is specified and used by the vehicle
manufacturer.
Figure 1-6. Every shop should have an assortment
of high-quality bolts and nuts to replace those damaged
during vehicle service procedures.
NUTS
Most nuts used on cap screws have the same hex
size as the cap screw head. Some inexpensive nuts
use a hex size larger than the cap screw head. Metric
nuts are often marked with dimples to show
their strength. More dimples indicate stronger
nuts. Some nuts and cap screws use interference fit
threads to keep them from accidentally loosening.
This means that the shape of the nut is slightly distorted
or that a section of the threads is deformed.
Nuts can also be kept from loosening with a nylon
washer fastened in the nut or with a nylon patch or
strip on the threads. See Figure 1-7.
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