Tuning pins are slender metal rods that secure the piano strings and enable precise tuning. Each string is anchored at one end to the cast iron plate (commonly referred to as the frame) and at the other end to the tuning pins, which are embedded into the vertical beam at the back of the piano. By turning the pins, the tension of the strings is adjusted, which raises or lowers their pitch. These components are crucial for maintaining proper string tension and ensuring the instrument is tuned to the desired frequencies.

Early tuning mechanisms, such as those in the monochord, used strings fixed at one end and tensioned by movable weights. In bowed instruments, non-threaded wooden pegs served this purpose. The first metallic tuning pins appeared in harpsichords, crafted from thin metal rods flattened at one end to fit a tuning key. These early pins had diameters of approximately 2–3 mm. As string tension demands increased, thicker pins became necessary. Harpsichords, early pianos, and similar instruments employed pins with a thickness of around 5 mm due to relatively lower string tensions. During the 19th century, flat or rectangular-headed pins were commonly used in table pianos. By the 18th century, threaded pins were introduced to enhance friction and stability. Modern tuning pins are robust and precisely engineered to handle the high tension of contemporary piano strings. 

High-quality tuning pins are manufactured from steel, with a torsional strength of 80–90 kg/mm². Nickel-plated pins are preferred for multilayer soundboards due to their durability and resistance to corrosion. Pins are typically inserted to a depth of 30 mm, with at least 24 mm embedded within the multilayer wood. The exposed portion of the pin, measured from the plate to the string attachment hole, should not exceed 11 mm. Properly installed pins should rotate smoothly without noise or deformation. After the strings are installed and tuned with triple leveling, the pins should offer a counterclockwise rotational resistance of no less than 1.4 kpm. The angle of pin inclination relative to the soundboard ranges between 92° and 96°. Their arrangement must ensure the strings are properly spaced to avoid contact with one another, ensuring optimal functionality and sound quality.