Square D (Schneider Electric) ZB4BD922 Harmony Head and Mounting Base. Schneider Electric Harmony™ Head and Mounting Base, Non-Illuminated, Series: ZB4, 22 mm Dia, Round, Metal. Additional Description: SQD -ZB4BD922 POTENTIOMETER MOUNTING COLLAR. Catalog Description: Harmony XB4, Potentiometer head, metal,black, Ø22, for use with Ø 6.35 mm shaft.