A truss rod is a metal rod that runs inside the neck of a guitar, providing structural support and allowing for adjustment of the neck’s relief. Relief refers to the curvature of the neck, which can be adjusted to suit the player’s preferences or to compensate for changes in string tension or humidity.
Tightening a truss rod involves turning it clockwise, which reduces the amount of relief in the neck. This is typically done when the neck is too bowed or concave, causing the strings to buzz against the frets. Conversely, loosening the truss rod (turning it counterclockwise) increases the relief, which may be necessary if the neck is too straight or convex, causing the strings to have high action (be too far from the frets).
