BlackSmith acoustic guitar strings are made with the finest materials and manufactured using state-of-the-art automatic servo controlled winding equipment. USA made phosphor bronze and steel ensures a long lasting string with increased sustain and purer & warmer tone. Sub-Zero treated plain steel strings offer brilliant tone with a silky feel. With BlackSmith acoustic guitar strings, you will experience the perfect balance of consistency, tone, and playability. Vacuum Sealed in Patented Anti Kink Packaging Prevents Oxidation and String Damage. PB-1152 - BlackSmith original "hybrid gauge" Phosphor Bronze acoustic set, for players who want a warmer tone in a comfortable combination of gauges that offers the depth and projection of light gauge bottom strings, but slightly less tension on the plain strings for easy bending.