These end caps are hand carved from engineered stone - Chrysocolla. This stone has varied shade of blue with some black veining running through the pattern. The pair pictured have a 6mm opening, but this item is available in virtually any size. If you need a size not listed here, just let us know - we can make it.
Each end cap is approximately 1 inch long and the narrow end has a 1/16" hole (large enough for several threads to fit through).