2, general G (gauge) corresponds to the outer diameter. The inner diameter varies according to the type of needle. The same G number, the same outer diameter, but thin-walled needles than thick-walled needle inner diameter is larger. Therefore, there is no absolute correspondence between inner diameter and gauge in the table below. It's just a characteristic of a certain type of needle itself. Just remember the outer diameter. Commonly used needles are as small as 31G and as large as 16G.
The following table is not exhaustive. But I hope that some friends have reference value.
Common domestic specifications are:
26G 25G 24G 23G 22G 21G 20G
0.45# 0.5# 0.55# 0.6# 0.7# 0.8# 0.9#
Brown Orange Orange Medium Purple Dark Blue Black Dark Green Yellow (shank color)
22G is a size 7 needle in China! 3! 28G is 3.5! 27 is 4! 26 is 4.5! 25 is 5! 24 is 5.5! 23 is 6! 22 is 7! 21 is 8!
I hope this helps!