Tuning keys are small tools used to adjust the tension of strings on musical instruments, such as guitars, violins, and pianos. They help musicians achieve the correct pitch by tightening or loosening the strings, ensuring the instrument sounds harmonious. Typically made of metal or plastic, tuning keys come in various shapes and sizes, depending on the instrument. For example, guitar tuning keys are often located on the headstock, while piano tuning keys are used to adjust the tension of the piano strings inside the instrument. Proper tuning is essential for optimal sound quality.