Martin Acoustic SP Bass Strings Medium 45-105 (4 strings) are ideal live, in the studio, or wherever maximum string life is desired. The creation of these high-performance replacement strings is a result of research done in cooperation with specialty steel producers. Due to the development of their ultra-high quality steel core, Martin SP guitar strings resist breakage better than average strings. In addition, both the core wires and the plain guitar strings are plated with a smooth, acoustic bronze finish. Though this golden bronze finish does enhance the beauty of your guitar, its purpose is much more functional—to prolong brightness, guitar string life, and superior tonal quality to meet the high expectations of demanding musicians.