I've been using these needles for small-scale piecing and like them very much. I think if they got much finer, I wouldn't be able to thread them. "Sharp" needles (as opposed to "universal") are recommended for straight stitching on cotton. The smaller size makes a smaller hole in the fabric. For needles sizes, the lower the number, the finer the needle. Instructions for my Singer Featherweight say to change the needle after every 8 hours of piecing!
NOTE: If you depend an a needle threader on your sewing machine, it may not work with this needle.