Piano wire, or "music wire", is a specialized type of wire made from tempered high-carbon steel, also known as spring steel

 General-purpose, high-carbon steel, drawn music wire (such as ASTM A228) is manufactured in both inch and metric music wire gauges (m.w.g.) in diameters as small as 0.15 mm up to 4.8 mm (0.006 to 0.192 inch). A small number of companies produce the tough, high tensile polished wire intended for limited music instrument markets, which is manufactured from steel of a specific composition by cold drawing. Unlike many other forms of wire, piano wire has no twist and is not formed from bundles of smaller-diameter wires.

Piano wire is also used in the fabrication of springs, fishing lures, special effects in the movie industry,[4] scaffold cross-bracing, orthodontic and pharyngial surgery, and for the cutting of cheese and soap. It is also commonly used in hobby applications such as model railroading, both control line and radio-controlled aircraft