Clam shell rings are a common currency form among the Abelam, Arapesh and Boiken peoples of the Sepik River region. The rings exist in diverse sizes and forms. All rings over four centimeters in diameter are used as money; smaller ones are only jewelry. The rings are all the more valuable the greater their diameter, the narrower the ring itself, and the more flawless and translucent their surface: this is because of the greater labor used to make them and of the higher risk of breaking them during the process. Yua clam shell rings circulate as money among the Abelam people. They supposedly learned their manufacture from the neighboring Arapesh. The Arapesh use the rings to buy pigs from the Abelam, and the Abelam measure their wealth in yua rings and use them for bride price and atonement payments.