How to choose signet ring top size?

We typically make the top of the signet ring, sometimes called the 'head' or the 'face', in two sizes.  The size shown is for either the diameter (for a round) or the height & width (for an oval) and is given in millimeters.

Typically larger top sizes work well for middle and ring fingers.  Smaller top sizes are normally great for a man or a woman's little finger, or for the ring finger of a smaller hand.