DaDawg is of course correct, I just wanted to add that it will also depend on how large you are and how much fat you have on you. If you are a very low bf%, you have less to worry about in terms of penetrating deep enough into the tissue. The more fat you need to cut through, the longer a needle you will need. I use 1" all over, but I also only weigh 185 and have very little BF.