2 Thick knows hsi stuff on this one.
I would add a point or two.
I am NOT into needles. At ALL. Its not about pain or anything ..... its the idea... so for me, making the injection as easy as possible is a BIG deal.
I initially checked into this, surveyed a lot of people, and the consensus was to use 23G, 1.5" for Glutes incections.
I was able to get 22G rather easily. And only 1" long.
I was a bit worried that the 22G would be noticeable larger than 23, so continued to work towards getting 23's. However, the 22s are just fine.
Plus, for me, I am using 1" in Glutes, and it has worked out fine. I think with Sust, given that it can hurt a bit, maybe be able to go deeper is better ......... but for the Test Cyp I have - its fine.