A piece of deformable material placed between rigid flanges or engine blocks to prevent fluids or gases from escaping under pressure. As the joint is bolted together, the material yields and flows into the microscopic imperfections of the metal. They are cut from rubber, silicone, soft metals, or composite sheets depending on the temperature and chemical exposure.
Heard on the job
Scrape the old gasket off the manifold flange before you bolt the new one on, or it will leak coolant.
Insider tip
Never reuse a crushed gasket. Once the material yields to the shape of the flanges, it loses the elasticity needed to seal a second time.