Ernie Ball 2721

2721 Cobalt Regular Slinky Electric Guitar Strings 12 Pack. Ernie Ball 2721 Cobalt Regular Slinky Electric Guitar Strings are a new spin on Ernie Ball’s best selling set of strings which have been played by the likes of Eric Clapton, John Mayer, Steve Vai and many more. The Cobalt Series is clearly an improvement on its classic nickel-wound counterpart giving the player increased sustain, clarity and output. In addition, they resist sweat and moisture better and have unmatched flexibility when compared to other nickel wound strings. “Ernie Ball Cobalt Strings sound and feel better than anything I’ve ever played!