Truss rod

A metal rod set into a channel in the neck, whose tension counteracts the pull of the strings and allows relief to be adjusted.

The common single-action rod can only straighten a neck that is bowing forward, while a double-action design can push it either way, which makes it useful on necks that would otherwise back-bow. The rod runs the length of the neck and is anchored at one end, with an adjusting nut accessible at the headstock or the heel. It adjusts relief, and cannot fix a twisted, warped or unevenly worn neck.

Example: a guitar with a working double-action rod can be kept straight through a year of changing humidity without structural work.

Truss rod

See also