A support bar for adjustably mounting accessories such a theatrical lamps wherein the bar is preferably formed of extruded aluminum and the bar is hollow with a closed interior electrical raceway for electrical cables extending the length of the bar and is isolated from a quadrilateral opening extending the length of the bar that communicates with the quadrilateral opening and the exterior of the bar. Adjustable mounting means extend from the lamps into the quadrilateral opening to mount the accessory and to allow sliding movement thereof within the bar.