Round Wound The most popular and universal construction, Round Wound strings deliver the traditional textured feel most players are familiar and comfortable with. Nickel-plated Steel Renowned for their distinctive, bright tone, XL nickel-plated steel is the industry standard for many genres and playing styles. Hex Core D'Addario Nickel Wound strings are wound with nickelplated steel onto a carefully drawn, hexagonally shaped, high carbon steel core. A high carbon steel alloy that is six-sided in cross section. When usedas the core or â€œcenterâ€ of a musical string, the 6 edge points firmly grip every turn of the wrapwire, ensuring a tight wrap and longer-lasting string. The D'Addario Difference It all starts with our exclusively engineered and built string winding machines. There is literally nothing like a D'Addario string machine. The combination of the most advanced computer-controlled winding technology and stringent incoming wire inspection delivers unmatched consistency, string after string, set after set. Every D'Addario string is made in the USA, ensuring the highest quality and performance.