Abstract: A device for affecting deflection control of an elongated stringed musical instrument neck or shaft is provided to compensate for undesired neck deflections. The device includes a substantially rigid sleeve which is carried within and extends along the neck. At least one core element is removably positioned within the sleeve. A control element is adjustably secured to the sleeve and cooperates with the core element or elements to exert deflection control forces on the sleeve. The sleeve in turn, imparts such deflection control forces to the elongated neck or shaft in which it is carried.