The instrument material "gold brass" has a higher copper ratio (85% copper + 15% zinc) than yellow brass. It has a relatively heavy feel when played and produces a rich, wide tone. Each metal has its own natural frequency (resonance frequency), and the vibration damping behavior differs depending on the metal. In other words, each metal material has a frequency that resonates easily. Because it resonates widely from high to low frequencies, it produces a very wide and deep sound. By using copper for the bridge, the characteristics of copper are added to the vibration energy to bring it closer to the sound of gold brass and transmit it to the instrument. The [HAMMERED] model not only has a beautiful, diffuse reflection pattern due to the hand-hammering process, but also hardens the metal. This allows vibration energy to be transmitted more effectively than in the normal model. Hammering is a processing method also used in accessory engraving, such as for rings. After hammering, polishing will remove the edges of the beautiful pattern. At our workshop, we perform hammering after polishing. Although this increases the number of steps, it creates a beautiful hammered pattern that retains the edges. Because it is a hand-hammered process, each product has a unique pattern. I purchased it hoping for a change in tone, but it didn't produce the tone I was looking for, so I am selling it. I have only used it twice. The plating is slightly peeled off, but it should not affect use. It comes with a box and a cloth. Thank you for looking.