It also depends on your choice of thread. Star thread is a little thicker & Bernina lady said to always use a 14/90 needle with it. Aurfill is so fine (and beautiful !) I use a 12/80 with that. cotton covered poly sometimes requires a 14 needle also. and batiks require a change of needle more often so they are sharp. I think there are a couple of internet sites that really explain needles, scarf, etc.