Fluoroelastomer Specialists
Sometimes it IS simply a matter of matching the damaged O-ring to a new O-ring from the box of assorted SAE O-rings you bought at the local auto parts store. Problem solved. But what if you can’t find an exact match in the SAE box, or the original O-ring is a weird color or has flat sides?
That’s when you enter the world of SAE vs. metric O-rings, special compositions and special designs. A world where metric O-rings are fractionally smaller in cross section than SAE O-rings, where the difference between Nitrile, Viton and Buna-N is the difference between leak/no leak, and where O-rings with round, square and x-shaped cross-sections are not interchangeable.
In general:
SAE O-rings and metric O-rings are generally not interchangeable. Using a small-diameter metric O-ring in the oversize groove of a SAE fitting often causes leaks because the smaller O-ring doesn’t compress properly. Similarly, an oversize SAE O-ring in a smaller grooved metric fitting is so big that it may get cut or crimped when the fitting is tightened.
O-rings that fit in a groove AROUND a fitting are generally SAE. O-rings that fit in a groove in the flat-faced END of a hydraulic fitting are generally metric. They’re often sold specifically as “Flat Face O-rings.”
If an O-ring is brown, white or a color other than black, it may be a special composition designed to withstand exposure to unique chemicals or designed for higher or lower than normal pressure ranges. Consider those colors warning that a special O-ring is required.
O-rings with square cross-sections are often used in unique applications. O-rings with an X-cross section are a variation on this design.
