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APPENDIX
FASTENER IDENTIFICATION
Fastener Selection and Installation
Selection and correct installation of threaded
fasteners are essential parts of any assembly or
rebuild procedure. Fasteners hold much of a
vehicle together. If a fastener fails to do its job
properly, it can cause a minor problem such as a
loose mirror, or a large problem, such as loss of
steering control.
Because there are so many styles of fasteners, in
various sizes and quality grades, a mechanic
must have a working familiarity with the fasteners
commonly used in vehicles. Only in this way can
the correct selection and installation of the proper
fastener be ensured. Each fastener is intended to
do a particular job, and is selected by the vehicle
manufacturer for its suitability for that job.
Equally important as the selection of the correct
fastener is its proper installation. Improperly
installing a correct fastener is just as bad as using
an incorrect one. Undertightening and
overtightening both result in an improperly
installed fastener. When threaded fasteners are
tightened, a slight stretching of the fastener
occurs, and it is this elongation that binds the
assembly together. If too little tightening occurs,
the slight stretching does not happen, and the
joint is not clamped securely. If too much
tightening occurs, the fastener will be stretched
too much, causing narrowing of the fastener and
possible breaking. Correct and consistent use of
a torque wrench will ensure that the fasteners are
properly tightened, and therefore are clamping
the pieces of the assembly together properly.
586
Figure 586 — Fastener Grading System
5-111.bk Page 508 Monday, July 10, 2006 2:26 PM
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