This is stitch number 9. It is very thin. It's the kind of needle specially used for embroidery.

I remember when we were young and married, the pillowcases were all made by ourselves, and the flowers on them were embroidered by ourselves. At that time, there were all kinds of embroidery patterns in the shops. When we bought the embroidery needle, we bought the size 9, which is a little longer than the ordinary size 9 needle. At that time, we were really original and patient, and we sewed thousands of stitches.