A ferrite material having a high Q value and also having a small absolute value of \u03b1\u03bcir in a wide temperature range between \u221240\xb0 C. In one embodiment, the device includes first and second sections and an intermediate section that together form an interior section. The tool is moved back and forth, in a condition where the bottom of the tool contacts the polishing object, while the strings are on the stringed instrument.