One size for drawing the oil up into the syringe, and then a thinner needle for the actual injecting. If you realize that the only thing that actually hurts is the original pinprick on the outer layer of skin, you'll realize it's not that bad. Once the tip is in, sliding it in further does NOT hurt. What hurts is later on if you don't rub the knots out. I found the ethyl oleate to be much better, much thinner, than any other kind. A lot of people have allergies to the sesame oil.