Application-specific dimensions of O-rings are specified by the tables in the relevant standards. Apart from this, there are generic metric dimensions of O-rings that have become established in general technical applications.
These are published in tables by the O-ring suppliers to facilitate selection and ordering.
The O-rings from a metric table do not have to be standardized dimensions. However, overlaps with metric standard tables are possible.
Even if O-rings from a metric table do not correspond to a standard size, the general rules for dimensioning can be applied to them.