Darco D2100 Xl Phosphor Bronze Acoustic Guitar Strings Extra Light String Gauges: .010, .014, .023w, .030w, .039w, .047w Tension: 133.3 Ball End 92/8 Phosphor Bronze: This alloy is comprised of 92% copper, 8% tin and traces of lead, iron, zinc and phosphor. These strings produce a bright but slightly warmer sound than the 80/20. The phosphor in the alloy helps them to retain their new sound for greater consistency.