The diameter of the front is larger than about 3 mm at the thinnest point in the middle. Thus, the plug seems much bigger than it actually is!
The acrylic ring on the back is unscrewable.
Carbon is an artificial fiber-compound which stands out due to it's great cohesiveness and light weight is therefore used in space travel, automotive, car tuning and sports.
This article is available in different sizes. When used properly the jewelry is harmless but cannot be sterilized.