I was one who always thought you just used the same needle for everything. Boy, was I wrong. Here are some links to Schmetz needle website and some different things to learn about needles. Very educational.
http://www.schmetzneedles.com/education.html
http://www.schmetzneedles.com/pdf/ne...20ABC_GB_S.pdf
Hope this helps you as much as it did me. :D :D :D