Truss Rod

The truss rod is part of a guitar or other fretted, stringed-instrument used to stabilize and adjust the lengthwise forward curvature (also called relief), of the neck. Usually it is a steel rod that runs inside the neck and has a bolt that can be used to adjust its tension. The first truss rod patent was applied for by Thaddeus McHugh, an employee of the Gibson company, in 1921, although the idea of "truss rod" can be encountered in patents as early as 1908.