From what I've been able to gather, it's tapered "cones" of metal or plastic that are inserted into the pierced hole. As the "cone" is wider at one end, this wide end is what stretches the hole by creating very fine minute tears in the area around the pierced hole which do not hurt but takes a little time to heal.
Zophie, What a gorgeous stud!! Very well balanced for your ears.
I can see the stud not sitting flush on your earlobes. I do not know if people see it is not flush on your earlobes if they are looking at it from the side. Because it is screwback, you do not have to worry about it popping the back off.
The screws may not be a good "taper" because it is not smooth. Of course I don't know enough but in my experience, the screws actually hurt my earlobes if left in too long, and I think it's because the screw was actually irritating inside the back part of my earlobe. There's a chance the micro-tears when stretching will be a bit more jagged within the earhole then a smooth round taper/hole.... kwim?
Gee, I've edited more times than I wanted to.... is this another solution? I know when I have trouble inserting my posts, sometimes I tug at my earlobe a bit to stretch in order to see the pierced hole. Can you insert it that way?