Dash Size

The Society of Automotive Engineers (SAE) publishes Aerospace Standard 568 (AS568), which defines o-ring dash sizes and corresponding nominal size (inner and outer diameters) and actual size in inches and millimeters (inner and outside diameters). Dash size is a three digit number preceded by a dash that relates to nominal and actual o-ring size. The AS568 is a chart published by the SAE that shows dash sizes and their corresponding nominal and actual inner and outside diameters for standard (inch) o-rings.  For example, an o-ring with an actual inside diameter of 0.029" and an actual width of 0.04” has a dash number of - 001.