BS 1806, BS ISO 3601-1 and SAE AS 568 O-rings

Chart 50 O-rings

Our Chart 50 reflects the O-ring standards used in many countries, particularly those of the UK and USA.

On Chart 50 in our O-ring guide, the reference numbers highlighted in red indicate those sizes covered by:

  • BS 1806: Dimensions of toroidal seals (O-rings) and their housing sizes (inch sizes)
  • BS ISO 3601-1: Fluid power systems - O-rings Part 1: Inside diameters, cross-sections, tolerances and designation codes
  • SAE AS 568: American National Standard Aerospace size standard for O-rings

Although the basic range is in inches, the O-rings can of course be used for sealing metric dimensioned components. Our Chart 50 tables include suggested metric shaft and cylinder sizes for which each individual O-ring is suitable. (Note: these figures are NOT merely direct metric conversions of the inch sizes. Also, separate ranges of back-up rings are available for metric shafts and cylinders.)

BS ISO 3601 sizes and tolerances
BS 1806 has been superseded by BS ISO 3601-1 (dimensions) and BS ISO 3601-2 (housings), but BS 1806 is still widely referenced by industry. The size codes in BS ISO 3601-1 (non-aerospace) are, with a few exceptions, the same as BS 1806. However, there are two tolerance bands, Class A and Class B, with the tighter tolerances of Class A equating to BS 1806. Our Chart 50 meets the Class A tolerances.


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