The gold was made into the wedding ring by Wartski, a family jewelry business founded in 1865, the official royal wedding Web site said.
Elizabeth presented the Welsh gold to William shortly after his engagement was announced, the Web site said.
Wartski provided engagement and wedding rings for Prince Charles and Camilla Parker-Bowles for their wedding in 2005.
Kate's ring was carried to Westminster Abbey by William's best man, Prince Harry.
The couple decided William would not wear a wedding ring.