Gauges 13-17-26-34-45-56. Pre-Alloy Phosphor Bronze Acoustic Guitar Strings are high-quality, long-lasting strings. Pre-Alloys are bright and unusually well-balanced in tone (first) and volume (second). Entirely all-American alloy phosphor bronze acoustic guitar strings with great clarity and durability. Gauges 13-17-26-34-45-56 Bright, well-balanced tone and volume