20g is a great needle to use to draw. Not so big. I find that 18g tends to punch holes through the stopper. Not too small. I find that 23g takes forever to draw oil out with. If you are going to draw from 2 or more vials for your injection, it is ok to use the same 18g pin to draw up, for instance your test and then your Masteron, but after the session is over, be sure to throw out the pin and start fresh next time. Each time you take a pin out of the wrapper, it is sterile, but after it sits around, it can collect dirt and bacteria. The last thing you want to do is save that pin and push it into your vial, possibly contaminating your oil with dirt and bacteria. For the cost of a couple cents, use a new one each session. The last thing you ever want to do is increase your risk of getting an infection, deep within your muscle!