Titanium Threadless with Prong Set Birthstone Tops. Fits M0.9 16 gauge industry standard internally threaded jewelry. Manufactured out of High Polish Implant Grade Titanium (Ti-6AL-4V-ELI ASTM F136). Available in assortment – 24pcs (2 sizes (2.5mm & 4mm)), 12 colors in a pack. Some uses of birthstones trace back to as early as the first century. While many cultures associate certain stones with birthdates or Zodiac signs, the official connections were finalized in 1952. Today, you can show off your personal connection to these timeless stones!