O-rings are specified by calling out the o-ring size, and the compound.
O-rings are available in 349 sizes as set up by the Aerospace Standard 568 published by the Society of Automotive Engineers. These sizes are designated by dash numbers as shown on the 568 DASH Chart. For instance, an o-ring with an inside diameter (I.D.) of .362 + .007″ and a cross section (W) of .103 + .005 is designated as: “AS568-1IO.” For o-ring sizes other than standard sizes, specify the actual dimensions desired for the inside diameter (I.D.) and the cross section (W) when filling out the Seal Request Form. There may be a tooling charge for such non-standards.