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Truss Rod

In modern stringed instruments with necks, a truss rod is often incorporated to adjust the neck profile - that is the up and down bend of the neck along its length. The device is normally made of steel and will have one or two rods which stretch the length of the neck, set into a groove below the fingerboard. One end is fixed and a bolt at the other end is used to adjust the tension. Some early truss rods had no adjustment - they were simply steel reinforcement.

At its slackest, the neck is exposed to the full tension of the strings which may make it bow up. Tightening the truss rod will tend to counteract the tension and restore the neck to straight. In practice, a very slight bow ('relief') is desirable. They tend to be fitted to instruments such as steel string Guitar, Banjo and Mandolin where the steel strings put the neck under higher tension than nylon or gut.

The truss rod adjuster is normally under a small cover visible in the centre of the headstock near the nut. To adjust it, one usually requires a special key or wrench. Adjustment should be done by experts and is only ever done a little at a time.