Inside measurements are approximately: 5/16" wide and 1/4" deep
A poison ring or pillbox ring is a type of ring with a container under the bezel or inside the bezel itself that could be New to hold poison or another substance. They became popular in Europe during the sixteenth century. The poison ring was New either to slip poison into an enemy's food or drink, or to facilitate the suicide of the wearer in order to escape capture or torture.
Rings like this have been New throughout history to carry perfume, locks of hair, devotional relics, messages and other keepsakes, so they have also been known by other names. Artists would paint tiny portraits of loved ones, to be carried in what was called a “locket ring,” which was popular during the Renaissance. By the 17th century, jewelers were creating locket rings in the shape of caskets which served as mementos for mourners. These were called “funeral rings.” Rings with compartments are also called “box” rings or “socket” rings.