The D'Addario EJ21 XL Nickel Wound electric guitar strings are the company's most popular round-wound jazz strings, with great resonance and tone, and a wound 3rd that's great for down-tuning. D'Addario's hex-core and and precision nickel-plated steel winding give the EJ21s a long lifespan and a bright, lively tone that works for all sorts of music and playing styles.