visit Superior Threads web site- they have free charts you can print off that tell you all the differences in threads/needles and what to use for what-
50wt is finer than 30 wt-
12 wt is almost a string- 100 wt is very fine- usually a silk thread
many people use 40-50 wt threads for most of their sewing needs.
cotton vs poly is kind of a personal choice- along with what you are doing-
cotton thread doesn't work so well with long-arm machines- the machine goes too fast and the thread breaks alot-
aurifil is a popular thread by many quilters.
but visit the site and learn the differences in threads and needles- then choose what works for you
