Phosphor Bronze was introduced to string making by D'Addario in 1974 and has become synonymous with warm acoustic tone. These strings are acclaimed world-wide, because they sound great even after extended use and wear. D'Addario Phosphor Bronze Acoustic Guitar Strings Features at a Glance: Custom Light Gauge .011, .015, .022, .032, .042, .052 Warm tone Phosphor bronze D'Addario's phosphor bronze acoustic guitar strings combine great sound with long life!