Borosilicate glass or "boro" is created by adding boron to the traditional glass maker's frit of silicate sand, soda, and ground lime. Referred to as "hard glass" because of it's durability and significantly higher melting temperature.
These will add a nice touch to any necklace especially if you are integrating any glass beads or enamel into your work!
No two pieces are alike and they are handmade, so they will not be machine- perfect.
The toggle or open ring is approximately 20-23mm and the pin is approximately 40mm.