DIN ISO 3601-1:2013 - Fluid power systems - O-rings - Part 1: Inside diameters, cross-sections, tolerances and designation codes (ISO 3601-1:2012 + Cor. 1:2012)
O-Ring Size Charts: AS568 & Metric | Global O-Ring and Seal
History of the ISO 3601 Series of Standards for O-Rings - Fluid Power Journal