Here's a (rather poor) photo of some earrings I made a while ago.
The Woolmark studs can be worn alone, or any of the hoops, topazes
or amethysts can be attached. Additionally, the amethysts or topazes
can fit inside the hoops.
Both the hoops and the studs have closed rings into which the shaped
prongs (visible on the amethysts and topazes) fit. The hoops also
have prongs, but they are not visible in the photo.
The prongs are made of springy white gold, and the gap between them
and the mount is just a little bit smaller than the thickness of the
gold wire that forms the rings.
Regards, Gary Wooding