Abstract: The ends of a tapered glass capillary are secured in relatively movable mounting blocks for application of axial tension to the capillary. This mounting enables the capillary to be pulled taut so that its axis is straight to facilitate propagation of X-rays. The capillary is coated to provide flexibility and strength. The ends of the capillary extend into their respective mounting blocks, with at least a portion of each end being stripped of the coating material. A bonding material contacts the glass and the coating material and secures both to their corresponding mounting blocks to hold the capillary in place when tension is applied and to provide shear strength for the capillary wall.