The XL Nickel Wound range are D'Addario's most popular electric guitar strings, and are precision wound with nickel plated steel onto a hexagonal high carbon steel core. They have a long lasting, distinctive bright tone and excellent intonation, and are ideal for the widest variety of guitars and musical styles. EJ21 is D'Addario's most popular round wound "jazz" set, being of medium gauge. The EJ21 set features a wound 3rd/G string for greater resonance and a tighter feel. They are also great for down tuning due to their tight tuning stability, making them the ideal set for acoustic players who like to dabble with electric playing, as well as being perfect for jazz rhythm players.