D Addario s octave mandolin strings are designed for use with octave mandolins of various scales. The unwound strings are made from plain steel and the wound strings are phosphor bronze. Phosphor Bronze was introduced to string making by D Addario in 1974 and has become synonymous with warm bright and well balanced acoustic tone. D Addario Phosphor Bronze strings are precision wound with corrosion resistant phosphor bronze onto a carefully drawn hexagonally shaped high carbon steel core.