Shape and Surface Deviations for O-rings according to DIN ISO 3601-3

Norm DIN ISO 3601-3 defines permissible shape and surface deviations in O-rings. Permissible tolerances are classified into grade levels.

Grade N O-rings are used in general applications and satisfy the high demands on dynamic and static sealing. Grade S O-rings are designed for applications which require higher quality standards in regards to permissible deviations and surface qualities.

If an inquiry / order doesn’t include any information regarding shape and surface deviation, we will issue a quote / deliver per grade N. Grade S O-rings are available upon request.

The following table defines shape and surface deviations in o-rings per grade levels N and S:

Surface Finish

The O-ring surface shall be free from cracks, ruptures, blisters or other imperfections that are greater than the limits given in the above table when the unstretched ring is viewed under a ×2 magnifier viewer with adequate illumination.

Flow marks, non-fills and indentations within the limits of the above table shall not be allowed if:
  • There are more than three in any 25mm length of circumference

  • They interconnect

  • There are more than three that are separated from each other by a distance that is less than the maximum limiting dimensions of such imperfection