I bought this earring for my helix piercing and it’s perfect. Hugs my ear, screws into place and stays put. I bought the 6.5 mm and there’s a little bit of room so it does slide around a bit (the curve can end up flipped around after sleeping or other activities, but easy to flip it back). I’m not sure if the 5mm would be too tight but if you want a snugger fit you might go for the 5mm.