the smaller gauge the number the larger diameter the pin,the higher gauge the smaller diameter of the pin
I prefer using a 23 gauge for all of my injections
1" for delts,traps,quads,triceps,and calves
1.5" for glutes
if you use a 21 gauge pin for everyday injections(i.e. trenbolone,propionate,winstrol,etc)you're going to have quite a bit of scar tissue on down the road.just something to think about