Each needle has an American and European size to describe its thickness.
Needles sizes are written as European/American size.
There are also three "main" types of sewing machine needles: ballpoint, universal, and sharp point.
Use these for tightly woven fabric or topstitching.
Use with stretchy, knit fabrics to prevent fabric damage and skipped stitches.
The "jack-of-all trades" needle, these work well for most woven or knit fabrics.