Martin Lifespan Acoustic Guitar Strings Coated phosphor bronze 10-47 Martin SP Lifespan Phosphor Bronze Coated Acoustic Guitar Strings offer a bright, rich, and warm tone. Top artists use this 92/8 composition for live performances and studio recording due to its consistent, slightly warmer tone out of the box. The high tensile strength carbon steel round core wire creates increased durability, keeping your guitar in tune and in tone longer.The proprietary Cleartone treatment on all six strings protects from dirt and oils, delivering the longest possible life for these SP strings. Gauges:MSP7000 Extra Light 10-14-23-30-39-47