Darco by Martin Guitars.. Pay Less. Play More. The Darco line of acoustic strings promises quality, tone, and value in every pack. They are designed for the pros and priced for the working musician so every guitar player can afford to change their strings as often as needed to keep their guitar sounding new all the time. Darco D230 Phosphor Bronze Acoustic Strings, .013- .056 • MFSKU D230 • UPC 729789555548