These sewing needles are suited for lighter fabrics. It comes in two different lengths. 4/2 is shorter and 4/3 is longer. "4" traditionally means the needle is made specially for silk fabrics. (but you can use them for light cottons of course!)
The needle industry in Hiroshima dates back 300 years, and close to 75% of what is produced is exported outside of Japan. With those fine needles, you can sew through a fabric without catching a thread. They also have larger eyes for an easy threading and do not warp easily.
Please note that the colors you see on the screen may not be accurate as each monitor displays differently. Thank you for your understanding.