Whether it’s Tiffany or Costco, here’s what you need to know Reviewed by Margaret James Costco may not be the first store that comes to mind when you think about shopping for a diamond ring.

Customers can buy a Gold, Silver, or Black ring in sizes 4 to 15. The other finishes, including Brushed Silver, Stealth, and Rose Gold, are unavailable at Costco, but can be bought on Oura's ...