WASHER SEAL

Typically made of a soft metal such as copper or aluminum, it deforms under torque to fill surface imperfections and prevent fluid or gas escape. This washer should be replaced whenever the mating component is serviced—common applications include oil drain plugs, fuel line connections, and high‑pressure oil passage plugs. While often associated with Cummins ISX engines, its precise use should be verified using the appropriate Cummins parts diagram for your engine model.