So, I assume that such a stud could be as large as 12-13mm in diameter. Therefore, the stud will take up 6-6.5mm on each side of the piercing hole. So the second piercing should be at least 8mm away from the center of the first hole, so the jewelry in the first and second holes do not touch.
Correspondingly, what earrings go with double piercings?
Hoop and Stud Combination
Having played around with studs the easiest two piercing update is to wear a hoop earring in your second ear piercing. Hoops make a lovely feminine and stylish addition to your earring stack whether you’re wearing them on a lobe or a helix piercing which is slightly further along your ear.