Ernie Ball RPS Nickel Wound Electric Guitar Strings are made from nickel plated steel wire wrapped around tin plated hex shaped steel core wire. The plain strings feature a patented winding of brass wire that is tightly wrapped around the lock twist of the ball end string to minimize slippage and breakage at the ball end. RPS strings last longer and stay in tune better than conventional plain strings. Gauges .010, .013, .017, .026, .036, .046