A versatile four-way adjustable truss system in a stringed musical instrument is disposed uniformly within the instrument neck that provides or supports a fingerboard or fret-board on its top side. The bottom surface of the truss may be exposed along its full length and made flush with the bottom neck surface and smooth to the touch. The truss is made adjustable at both ends in either tension or compression and is securely fastened to the neck at an intermediate fastening point so as to form two substantially co-linear neck sections either of which can be adjusted independent of the other, via an associated adjustment nut constrained in a corresponding thrust cavity configured in the neck, to satisfy a desired section profile requirement in a range that includes both concave and convex curvature.