The thread used to make a piano is typically a high-quality, strong, and flexible type known as "music wire." Music wire is a specialized steel wire that is designed to withstand the tension required for piano strings. It is made from high-carbon steel, which provides the necessary strength and durability. The wire is then drawn through a series of dies to achieve the desired thickness and tension characteristics.

The choice of music wire for piano strings is crucial due to the demands placed on the strings. A piano has up to 88 keys, each with its own string, and these strings must be capable of producing a wide range of pitches and volumes. The tension of the strings is typically around 150 to 200 pounds per string, which requires a material that can maintain its shape and tension over time. Music wire is ideal for this purpose because it has a high tensile strength and can resist fatigue and bending.

According to a study by the Piano Technicians Guild, the average tension of a piano string is approximately 150 pounds, with the highest tension strings reaching up to 200 pounds. This high tension necessitates the use of a strong thread material like music wire. The flexibility of music wire also allows it to resonate effectively, contributing to the rich and complex sound of a piano.

In addition to its strength and flexibility, music wire is also resistant to corrosion, which is important for the longevity of the piano. Over time, piano strings can be exposed to environmental factors such as humidity and temperature changes, which can cause corrosion. The corrosion-resistant properties of music wire help to maintain the integrity of the strings and the overall performance of the piano.

In summary, the thread used to make piano strings is music wire, a high-carbon steel wire that offers the necessary strength, flexibility, and corrosion resistance to meet the demands of a piano's strings. The choice of music wire is essential for the production of a high-quality piano that can produce a wide range of pitches and volumes with clarity and resonance.