A bracelet, usually one produced before the mid-6th century. In the Jōmon period bracelets were made from bivalve shells, nimaigai 二枚貝, and in the Yayoi period shell bracelets, kaiwa 貝輪, were made from other types of shell such as the cone shell, imogai 芋貝, and the false trumpet shell, tengunishi 天狗螺. Hooked copper bracelets, yūhō dōsen 有鉋銅釧 were also made, imitating the shape of shell bracelets. The number and variety of kushiro was greatest in the Kofun period. Examples now in the Tokyo National Museum include copper and silver bracelets, some decorated with jewels and precious stones, and some with bells attached, suzukushiro or rinsen 鈴釧. There are five, six, or occasionally eight bells arranged regularly on a circular bracelet. Many round copper kushiro are engraved with ridges. Excavations of tombs, kofun 古墳, also uncovered distinctively shaped stone bracelets, ishikushiro 石釧, made of jasper: the wheel-shaped stone, sharinseki 車輪石, and the plough-shaped stone, kuwagata-ishi 鍬形石. These were not worn as bracelets but used as funerary offerings. Ancient Korean tombs contain many engraved gold and silver bracelets, and in China simple round bracelets of gold, silver, and copper known as sen 釧 (chuan in Chinese ) or jōdatsu 条脱 have been recovered from Han dynasty graves.