The 16" is really only good for the bottom of hat. You will probably have to choose another method of knitting in the round - DPN, Magic Loop, or two circular needles the same diameter. Check the video section for help if you don't know how.
I will say here that many people do not like 12" circulars. They are much harder to knit with because the needles are very short because of the short cable. My preferred method is Magic Loop, but I've also used the other methods. the length of the cable for ML depends on what you're making, but I like a 40" for most things.
What are you making. Knowing that helps.