GM Genuine Parts HVAC Heater Pipe O-Rings are designed, engineered, and tested to rigorous standards, and are backed by General Motors. These O-Rings are elastomer that form a water-tight connection between the heater pipe and engine. 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).