Body Jewelry and Belly Button Rings are measured by gauge and diameter. Gauge measures the thickness of the metal. The higher the number the thinner the metal. (See chart below for common gauges used in body jewelry). Some people are surprised at the thickness of jewelry suggested for some body piercing. When jewelry thinner than suggested is used, the body can mistake it for a foreign body and reject it, pushing it to the surface of the skin and healing it out. Also very thin gauges can be dangerous. If the jewelry gets tugged on, or accidentally caught on something, it can result in a nasty cut or even slice through the skin.