14k plain heart threaded stud. Very flat against the skin.
6.5mm (1/4") fits an average helix or upper cartilage
5mm (3/16") fits a thin helix or upper cartilage. This length also works in the middle cartilage area: the area in between the lobe and cartilage which is thin. If a traditional ear stud sticks out from its backing in your lobe then your cartilage is thin and 5mm is your size.