Pioneering innovative string design has been a D'Addario family tradition for nine generations. Most guitar players don't realize that the inner core wire in all D'Addario steel strings is made from carefully drawn, hexagonally shaped, high carbon steel wire. The 6 "edges" of the core wire bite into the softer wrap wire, securing it all along its length. The hexagon core is just one of the reasons D'Addario strings are "Better by Design." Hexagonally shaped high carbon steel core wire. Core wire edges dig in to the wrap wire to ensure a tight bond between the core and the wrap wire.