The size 3.0 is about 20% smaller than the factory needle for your machine. Can be used with tiny or smooth threads such as Superior’s Sew Fine(tm) or Magnifico or Fantastico, or Glide from Fil-tec. It makes a smaller hole which can be an advantage on batik fabrics. It will have significantly more gap between the needle and the hook point (an additional 0.10 mm), so if skipped stitches occur, change back to the regular size 4.0 needle. If the needle is too small for the thread you are using, it can also appear as though your top tension is too loose (symptom will be consistent pokies on the back of the quilt, not just once in a while but on every single stitch) – if this happens suddenly after switching to this very fine needle, you need to either use a larger needle OR change to a finer, smoother thread.
These are SHARP needles (designated R on the package) for regular quilting on cotton and batiks.
This is the pack of 10 needles.
(image is of the 4.0 size needles but just because I was too lazy to photograph all the different packages)