The first part we ever worked with was the O-ring back in the 1950s. It is the most common fluid seal, called “O” for its round cross-section profile. O-rings create a seal at the interface between two or more components where they are seated in a groove and compressed during assembly. They perform well in both static and dynamic applications. They are simple and basic items, but that doesn’t change how critical their performance is in a variety of applications. If there’s air, gas, or fluid in it or flowing through it, there are O-rings in it. Often, O-rings are among the lowest cost components in the application, but will likely be the most visible should they fail.