Abstract: A steel rod of the type having a generally rounded core and two or more spaced series of parallel ribs projecting therefrom, so constructed that the ribs act as threads to attach the rod to an anchoring or connecting device which has matching internal threads, is provided which in addition to the rib structure has a longitudinal groove in at least one of the regions between the adjacent ends of two of the series of ribs. The longitudinal groove or grooves provides a canal which permits the cavities between the rod and an enveloping anchoring or connecting means to be filled with cement or similar material which will protect the internal surfaces against corrosion.