Gauges 12-16-25-32-42-54 Martin M140 Light Acoustic Guitar Strings have an 80/20 composition for brilliance, clarity, and longevity of sound. The Bronze winding alloy is ideally suited for making strings have deep, rich basses and clear, bright trebles. The Martin M140 acoustic pack has high-quality strings for daily use. Core and wrap wires meet strict requirements to make the grade. Martin guitar strings are wound to precise specifications.