I make these labrets by first melting sterling silver in to a ball that I then flatten and solder a smaller 18k gold ball on to it, I then flatten the gold ball slightly.
Finally I oxidize it black so the gold really stands out against the silver. All of this gives each piece a very unique and organic feel, no piece is alike.
They measure around 4mm in diameter but it can differ up to 0.5mm so if you're very specific about the size send me a convo and I will make one especially for you.
The bioflex post comes in 18g (only 6mm and 7mm) 16g or 14g and in a number of different lengths. The 3rd picture shows it with a 9mm 14g labret.