EJ21 features a wound 3rd string and is optimal for "jazz" style playing and some drop tunings. XL Nickel Wound electric guitar strings, long recognized as the industry standard, are ideal for a wide range of musical styles. XL Nickel Wound, D'Addario's most popular guitar strings, are precision wound with nickel plated steel onto a carefully drawn, hexagonally shaped, high carbon steel core. The result—strings with long lasting, distinctive, bright tone and excellent intonation—is ideal for the widest variety of guitars and musical styles.