Stand the test of time with strings that endure. D’Addario XT strings combine high carbon steel cores with an extended lifespan treatment on every string in the set, giving you enhanced break resistance, pitch stability, and long-lasting performance – all while preserving the tone and feel of your favorite uncoated strings. These strings are made to stay, for performance that never fades away. Phosphor bronze, custom medium gauge, 0115, 016, 026, 040 (x2).