The fact that the width/height of each o-ring is 1/16' means the OD is always 1/8' larger than the ID (1/16' on each side, making 1/8' total). The diameter of the o-ring is listed as follows: The o-rings being symmetrical means their heights and widths will be the same, as measured through a cross-section seen below.
Other AS standard sizes are thicker but these are uncommon within the paintball industry. All AS standard o-ring sizes that have only two digits have a 'height' of 1/16 inch, meaning the o-ring will be 1/16' high if you lay it down on the table. This number corresponds to a set of pre-defined sizes listed below. The first number in the AS standard designation is the o-ring size. The first number is the size of the o-ring, the second number is the durometer or 'hardness' (explained later). This is considered the AS568A standard, or simply AS for short, which is the most common method of classifying o-rings in the United States. Most non-mectric 'SAE' o-rings are listed in a two-number form divided by a slash (example, 12/70, 17/70, 12/90, 15/90, etc.). This page has lots of information, especially useful in cases of buying your own seals locally or from the internet. There seems to be an amount of confusion surrounding o-ring sizing and selection. O-ring Information > Tech index > O-ring info
