I have been doing my delts this cycle and I'm using a 5/8" 25g. Makes for slow injecting but I think it results in less PIP by injecting slower. I take a full minute to inject 1ml. I should also mention that I am very lean, if I had more chunk to me i would definitely go 1". I think i could easily use 1/2" and get it into the delt but I prefer it goes a little deeper into the muscle.