ISO 3601 Metric O-Rings Size
Issued by the International Organization for Standardization, the ISO 3601 standard contains of two groups of O-Rings, Class A and Class B. Class A corresponds to the American standard AS 568B in its current format (the 900 series tube fitting O-Rings are not included). The ISO 3601-1 Size Code for these O-Rings is the same as the AS 568 dash number. Class B allows production of O-Rings in technically acceptable and economical “metric” sizes, which can then fit into metric grooves.