Post-tensioning elements, namely, metal cable wires, steel strands and steel bars; steel ducts for housing of post-tensioning elements for use in pretensioned and post-tensioned concrete; metal post-tensioning cables for prestressed concrete constructions of all types as listed below, including suspended bridges and roofs; metal wedges; steel ground anchors and stay cable anchors for use in concrete and prestressed concrete; steel couplers; steel protection caps for covering the ends of the c...