In this product name, '50 mm' indicates the diameter of the ring-shaped pendant, meaning the distance across the circle from one outer edge to the other. That is around 5 cm or just under 2 inches, which makes it a medium-to-large pendant rather than a small charm.
Because the pendant has an open centre, it is a circle of stone rather than a solid disc. You will see the full ring when it hangs, and the cord passes through the middle. This shape keeps it visually simple and makes it easy to pair with casual clothes. The open centre also lets the cord or your skin show through, so the pendant does not look as heavy as a solid slab.
The exact way it sits depends on the length of the cord and how the knot is tied. On a typical cord it will hang around the upper chest area. It can be worn on its own or layered with longer necklaces if you want a more personal style.
As with most natural stone products, the surface may have slight differences in shading, gloss, or pattern between individual pieces, but the 50 mm ring size remains the same.