Topic summary
Stone setting

Extracted from the Wikipedia article Stonesetting.
Cuts
Just as the angle of the sides of a cabochon creates the pressure to hold the stone in place, so there is an overlying principle in setting faceted stones. If one looks at a side view of a round diamond, for example, one will see that there is an outer edge, called the girdle, and the top angles up from there, and the bottom angles down from there. Faceted stones are set by "pinching" that angle with metal. All of the styles of faceted stone setting use this concept in one way or another.