Metric dimensions originate from the international metric system of units and are given in millimeters.
Inch dimensions originate from the much older Anglo-American measurement system and are given in inches.
Note: In accordance with the international standard, the O-ring dimensions are now specified in millimeters.
Converting inches into millimeters (mm) produces the odd numbers you are surely familiar with.
Example: 20.35 x 1.78 mm (0.801 x 0.07 inch)
Technical article on standardized O-ring dimension lists | Sealing Academy | Click here >>