A truss rod apparatus, for use within a stringed musical instrument, to correct both forward and backward bowing of the instrument's neck. The apparatus includes an elongate rod with an adjustor mechanism incorporating two axially oriented threaded sections of similar thread direction but differing thread pitches. In use, the adjustable rod is attached near its ends to a second elongate member. Turning the adjustor mechanism in either direction causes the threaded sections to advance at different rates, thereby causing a slight change in length of the rod. The change in length relative to the second elongate member, induces a bending force on the apparatus which in turn induces a corrective bending in the neck of the musical instrument into which the truss rod apparatus is embedded.