ISO 3601

Global O-Ring and Seal is fully compliant to the dimension and tolerance standards spelled out in ISO 3601-1 Class A for all standard series O-rings and Class B for all metric series O-rings. Subsequently, Global O-Ring and Seal defines the quality acceptance criteria of all O-rings to be in accordance with ISO 3601-3 Grade N which classifies surface imperfections and specifies maximum acceptable limits for these imperfections. This information can be viewed in PDF format here. Stricter tolerance and inspection requirements can be achieved upon customer request.

ISO 3601-1: Dimensional Tolerances

ISO 3601-1 states two classes of O-rings: Class A and Class B. Class A O-rings have equivalent tolerances to those used in AS568, which are tighter than the tolerances for Class B O-rings, and are suitable for industrial or aerospace applications when the application or the housing require tighter tolerances. Class B O-rings have slightly wider tolerances and are suitable for general-purpose applications.

ISO 3601-3: Quality Acceptance Criteria

ISO 3601-3 was originally developed for general-purpose O-rings, but over the years this standard has been revised and refined to include three grades (N, S, CS) of defects depending upon the application.

Grade N: The standard of acceptance for general-purpose O-rings.

Grade S:  Quality requirements for optimum performance industrial applications and aerospace applications.

Grade CS: Special and critical sealing applications, such as certain aerospace applications and critical oxygen service applications.

Examples of surface imperfections characterized by this standard include flash, offset, parting-line projection, back rind, excessive trimming, flow marks, non-fills, and indentations.

ISO 3601 Metric O-Rings Size Chart

Issued by the International Organization for Standardization, the ISO 3601 standard contains 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. The first digit of the Size Code indicates the cross section group (A-E), while the last four digits indicate the O-Ring inside diameter rounded to one-tenth millimeter.

For a complete listing of all metric o-ring sizes, visit our Metric O-Ring Cross Reference Table.


ISO 3601 Size Chart

Global Part # Reference C/S (MM) I.D. (MM) C/S (Inch) I.D. (Inch)