Medium nickel wound electric guitar strings. Electro-Harmonix electric guitar strings are custom-designed to our specifications and made in the USA by a premiere string manufacturer. Each wound string is precision wrapped with round nickel-plated steel onto a high carbon, hexagon-shaped steel core. The plain strings are made from the same high carbon steel as the hex cores. The high quality steel and computer controlled winding process results in strings that intonate accurately, are better at staying in tune and vibrate evenly for maximum sustain.