Seals and gaskets provide a barrier against air, water, and oil leaks. The O-ring is the most common type of seal or gasket used in mechanical systems. They are shaped like the letter “O” and are used in hydraulic systems and on pipe, pumps, and cylinders. Another common seal is the oil seal. The oil seal prevents lubrication from leaking from a joint of a moving part. Key elements to consider when selecting seals and gaskets are the outside diameter, inside diameter, material, and operating temperature.