There are GB1235-76, GB3452.1-88 and GB3452.1-92 about the size of O-rings in China's national standards. The cross-sectional diameters (also called wire diameters) of O-rings specified in GB1235-76 are 1.9, 2.4, 3.1, 3.5, 5.7, etc., and O-rings adopt "outer diameter * wire diameter" G