Martin Msp4000 Sp Acoustic Guitar Strings Xl 3 Packs Extra-Light String Gauge: .010, .014, .023w, .030w, .039w, .047w The Martin SP Studio/Performance Series strings are ideal live, in the studio, or wherever maximum string life is desired. The creation of these new high performance strings is a result of research done in cooperation with specialty steel producers. Due to the development of an industry leading ultra-high quality steel core, Martin SP strings resist breakage better than average strings. In addition, both the core wires and the plain strings are plated with a smooth, acoustic bronze finish. 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. Ball End; Tension: 133.3