This is sooo important and I reckon most of the issues ppl post about on here with FMQ are down to not understanding this basic info so thanks for sharing. This is handy too if you use Superior like I do - it tells you roughly where your top tension should be thread by thread and also what needle to use.
http://www.superiorthreads.com/media..._HOME_7-11.pdf
Although I do use a slightly smaller needle than they recommend as a rule - but rules are made to be broken right? :mrgreen: The best advice is to experiment with every thread you'll ever use with different needles and tensions then keep a reference of what works best - though I find it can vary between types of batting and even fabrics, for eg batiks I use a finer needle in general. This is the science part of our art and there'd be a lot less frustrated quilters if more ppl took the trouble to learn it. Sorry, I'm dismounting from my soap box NOW! :lol: