i use the slin pins for b12 and use 25g 1" for my primo into the quads and 23g 1.5" for primo in glutes. even with the primo heated up a bit, it takes a while to push through the 25g pin, but I found that I can only push in so much at a time anyway. if i push too fast I can feel pain building up, so 25g works fine for me.