These are the fonts that can be engraved in your ring.  The fonts are scalable, so they can be made larger or smaller to fit.  A good rule of thumb is to keep the number of characters to around 32 or fewer.  Smaller rings will have less room, so fewer letters will be more readable.  The same goes for tension set rings, where there will not be as much room for an inscription due to the stone gap.  Wide rings will have the option of engraving on more than one line.  Some rings, such as Helixx, have geometry which is difficult to engrave, but may be possible if the number of characters is kept very small.