13-17-26W-36-46-56 Lenth 43 inches. Phosphor Bronze wound strings were introduced in the early Seventies and have become the most popular acoustic string. Phosphor bronze wire is made from approximately 92% copper, 7% zinc and 1% phosphorous. It took several years of trial and error to develop a proprietary string coating that resists tarnish and corrosion without compromising tonal quality. Phosphor Bronze provides nice highs and lows with pleasant subtle overtones. Phosphorous is used to help reduce tarnish and corrosion.