The difference between a G-string and a thong is that a thong has a wider band. A thong is believed to be sturdier than a G-string.
The terms "G-string" and "thong" are often used interchangeably. They are both considered to be pieces of lingerie. A G-string is used to serve as a cover and a way to give support for someone's genitals. It has a piece of cloth between the buttocks called a band and it is connected to a band that fits around the hips. The thong's band is usually one or two inches wider than the G-string band. The G-string band has the appearance of a string.