in a stressing anchorage for prestressing elements in part of a structure , at least one part of an anchor head consists of a mortar - like mass in the area in which bores are disposed to accept frustoconical wedges . the frustoconical wedges are made of steel . since the mortar - like mass on which the frustoconical wedges are supported is more ductile , i . e ., more workable than the wedges , the distribution of load from the wedges to the anchor head takes place in such a fashion that marked peaks of the load are considerably reduced .