Abstract: A stringed musical instrument that is convertible between fretted and fretless playing configurations includes a body, a neck connected to the body at one of its ends, a fingerboard disposed on the neck, a plurality of movable frets spaced apart at positions along the fingerboard, a plurality of strings disposed above the frets, and, according to one aspect of the invention, at least one rod that extends through the frets, wherein the at least one rod is configured to function both as a spring and as a device for retaining the frets in the fingerboard. According to another aspect of the invention, at least one strip of material separates a metallic component of a fret adjustment device from another component of the instrument that is formed from metal, wherein the at least one strip of material is configured to provide permanent dry lubrication for the metallic component of the fret adjustment device.