The D'Addario EJ17-3D Phosphor Bronze Medium Acoustic Guitar Strings pack gives you three sets of EJ17s and saves you money. EJ17s offer heavier tension resulting in a bolder, more resonant acoustic tone with higher resistance for heavy strumming and flat-picking. Phosphor Bronze was introduced to string making by D'Addario in 1974 and has become synonymous with warm, bright, and well balanced acoustic tone. D'Addario EJ17-3D Phosphor Bronze Medium Acoustic Guitar Strings are precision wound with corrosion resistant phosphor bronze onto a carefully drawn, hexagonally shaped, high carbon steel core. The result is long lasting, bright sounding tone with excellent intonation.