O-Ring Size Measurement Specifications

To measure an o-ring, you can just measure its inside diameter (ID) and cross section (CS) (also call width or thickness). The outside diameter (OD) can be known according to the formula: OD = ID + CS*2. The above AS568 o-ring reference chart not only shows the ID and CS but also shows the OD and part dash number. These full specifications are for your fast-looking up and comparison.

The AS568 O-Ring Size Chart is issued by the Society of Automotive Engineers (S.A.E.) which is the most commonly used o-ring size in the USA. This standard specifies the inside diameters, cross-sections, tolerances, and size identification codes (dash numbers) for o-rings used in sealing applications and for straight thread tube fitting boss gaskets. The dimensions and tolerances specified in this o-ring seal standard size table are suitable for any rubber elastomeric materials, e.g. NBR / Buna-N / Nitrile, Silicone, EPDM, FKM / Viton®, Kalrez®, etc. and for sizes from micro to large provided that suitable tooling is available.