User Manual

200 SPECIFICATIONS
Page 2-5
FASTENER TORQUE
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.
Proper installation is as important as the selection
of the correct fastener. 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
stretching 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
excessively stretched, causing narrowing of the
fastener and possibly breaking. Correct and
consistent use of a torque wrench ensures the
fasteners are properly tightened, and clamping
the pieces of the assembly together.
Figure 2-1 — Fastener Grading System
5-101.bk Page 5 Friday, March 17, 2006 11:05 AM