How are the specifications of sewing machine needles described and what do they mean?

Sewing machine needles are divided into metric system and gauge system (American system) according to industry regulations. Whether it is metric or gauge system, it is based on the diameter of the working part of the needle as the number of needles. The type of sewing machine needle refers to the thickness of the needle. The thicker the needle, the thicker the material, and the thinner the needle, the thinner the material, and the length remains unchanged. See below for comparison:
1. Metric sewing machine needles of No. 60 and No. 8, working part diameter 0.60mm, thin, for fabrics (such as silk fabrics)
2. Metric sewing machine needles of No. 65 and No. 9, working part diameter 0.65mm, thin, for fabrics (such as silk fabrics)
3. Metric 70, No. 10 sewing machine needles, working part diameter 0.70mm, for medium to thin fabrics (such as shirts, sweatshirt fabrics)
4. Metric No. 75 and No. 11 sewing machine needles, working part diameter 0.75mm, for medium to thin fabrics (such as shirts, sweatshirts)
5. Metric 80, 12 gauge sewing machine needles, working part diameter 0.80mm, for medium to thick fabrics (such as spring and autumn jacket fabrics)
6. Metric 85 and 13 sewing machine needles, working part diameter 0.85mm, for medium to thick fabrics (such as spring and autumn jacket fabrics)
7. Metric sewing machine needles of No. 90 and No. 14, working part diameter 0.90mm, for thick fabrics (such as jeans fabric)
8. Metric 100, No. 15 sewing machine needles, working part diameter 1.00mm, for thick fabrics (such as thick cotton fabrics)
Since household sewing machines were imported from the United States, it is still used to call the needle number of needles in the American system.