Darco D-230 phosphor bronze acoustic guitar string set 13-56. 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 guitarist can afford to change their strings as often as needed to keep their guitar sounding new all the time. Darco acoustic strings are meticulously constructed using a tin-plated steel core wire and premium quality wrap wire. Darco offers guitarists that pre-gig-peace-of-mind or heading-to-the-studio fresh set string change.