Abstract: A device for vulcanizing or cross-linking a cord particularly a cable provided with a plastic covering, the device comprising an elongated pipe housing at the upper end of the housing, the cord being inserted and the upper area thereof being defined as a heating area and the lower area thereof as a cooling area wherien at least the heating area is provided with an inlet and an outlet for a protective gas, and an inspection window fitting positioned laterally at the pipe housing adjacent to the upper end for inspecting or measuring, respectively, the diameter of the cord by means of a suitable optical-electrical measuring device through an inspection window, wherein a separate heating device is associated with the upper area of the heating area of the pipe housing associated with the inspection window fitting, the heating device heating the atmosphere in the upper area permanently to a temperature higher than in the remaining areas of the heating area.