22-23 g is the common, but 3/4 is too short. From the research I did before I started my first cycle, and from what I've been told by friends who are long time users of steroids, 3/4 is too short to deliver deep enough into the muscle, which can create problems like an abscess which can get infected and then you have a real problem. I've seen videos of abscess removals and they are no joke. The most common length is 1.5. I've seen really big guys use 2 inch, but for most people, 1.5 inch is plenty. I have also seen people using 1 in, but it was for bicep and pectoral injections. Even if you are skinny as a pencil, I think 3/4 is just too short.