take some things into consideration when choosing your pin, the higher the guage the smaller the tip, the less scar tissue, and the longer it will take for an oil based product to pass through 21, 22, 23 etc produce more scar tissue, but make the oil (test enant) easier to slip through so the injection will be quicker, if you dont mind the pin in you for however longer depending on how many ccs you use, go with a 25g, if you want it to be over with quick roll with a 22-23g...good luck