In our drop-down menus for adding to cart, we show the gauge of the item you are ordering, then the length/diameter, then the ball size if it has any:
14g - 3/4 inch (5mm balls) 6g - 1/2 inch (8mm balls)
Jewelry is measured through a gauge system (conversion chart below). The higher the gauge number the smaller the wire is. For reference, a standard "earring" is usually 20 gauge. Jewelry gauges can vary between manufacturers. There is no universal regulation on companies to make a standard size in body jewelry. This is because some jewelry is made outside of the USA and measured in millimeters. And in the USA jewelry is measured in inches.