Tip: O-ring Sizes

O-rings are available in standard sizes according to different industry standards. These sizes include the AS568 (Aerospace Size Standard of O-rings, 001-475), AS568 boss gasket sizes (Aerospace Size Standard of O-rings, 901 and up), JIS standard sizes, JASO standard sizes, AS871 and British Standard metric o-ring sizes.

In general, the inch-based sizes of the AS568 are considered to be the U.S. standard while metric o-ring sizes are for the rest of the world.

When a custom or metric o-ring is what is required then the inside diameter, outside diameter and width determine the size. Actually there are many different sizes, both metric and non-standard that are available through PSP.

Perhaps there will come a day when the metric system will become the sole measurement system in the U. S. and it will be a little easier to buy a metric o-ring here. There was a strong movement toward the sole use of the metric system during the 1970's and 1980's; however it lost its momentum. Currently there is a use of the dual measurement system in the U.S. However, the world gets smaller and smaller every day and the requirements of everyone outside of the U.S. for that little metric o-ring is having an impact.