EJ13 is a custom light gauge 80/20 Bronze set that features lighter top and bottom strings for ease of playability and balance. 80/20 Bronze, the original acoustic alloy introduced to by John D'Addario Sr. and John D'Angelico in the 1930s is a popular alloy for recording due to their crisp, deep and projecting tone and appeal to many traditionalists and vintage enthusiasts for their historical significance.