GM Genuine Parts Multi-Purpose O-Rings are designed, engineered, and tested to rigorous standards, and are backed by General Motors. These o'rings are used in some applications instead of paper or composite gaskets to seal engine components. The interface between components will have a machined groove to accept the O-ring. The O-ring is slightly compressed when assembled to provide a liquid-tight seal, keeping engine fluids in and air and dirt out. GM Genuine Parts are the true OE parts installed during the production of or validated by General Motors for GM vehicles. Some GM Genuine Parts may have formerly appeared as ACDelco GM Original Equipment (OE).