Abstract: In the attachment of a tension rod to an open end of a cable, one end of a tension rod is axially inserted into the core of the cable and the combination vertically positioned with the other end of the tension rod extending downward. A heat shrinkable plastic cap including a casting resin is moved up from below the tension rod until the inside bottom surface of the plastic cap comes proximate to the bottom of the tension rod, and the upper open portion of the plastic cap encompasses a section of the cable jacket. Heat is then applied to the upper portion of the plastic cap so as to shrink the upper portion to form a hermetic seal with the cable jacket, and then to the lower portion of the plastic cap so as to shrink that portion of the plastic cap toward the portion of the tension rod extending from the open end of the cable, so as to form a closed volume within the cap that decreases upon shrinkage to uniformly press the casting resin contained therein into the cable core.