 The
truss rod is an adjustable
metal rod that runs along the inside
of the neck,
adjusted by an allen-key bolt usually
located either at the headstock
(under a cover) or just inside the body
of the guitar,
underneath the fretboard
(accessible through the sound hole).
The immense amount of tension the strings
place on the neck
can sometimes bend it forward, and changes
in humidity can warp the wood slightly.
The truss rod allows the neck
to be adjusted to accommodate these
changes -- tightening it will curve
the neck
back and loosening it will return it
forward. Some truss rod systems, called
"double action" truss systems,
will tighten both ways, allowing the
neck
to be pushed both forward and backward
(most truss rods can only be loosened
so much, beyond which the bolt will
just come loose and the neck
will no longer be pulled backward).
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