DSB - your machine manual should tell you what needle to use for what kind of fabric - but I THINK the smaller the number on the needle, then the thinner fabric it should be used for - I use a 10, 11, or 12 for cottons, 14 for denim - if I'm going through several layers of cotton & batting, I go with the 12 - but you will probably get more ideas from other members here, I'm sure! Or you could do a google search too!