Seals and gaskets are used in a wide range of applications to provide a barrier against air, water, and oil leakage in addition to a host of environmental factors. One of the most common types of gaskets is the O-ring, which is a seal used in mechanical systems. As the name suggests, 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, which is designed to prevent lubrication from leaking and to prevent two or more fluids from meeting at the joint of moving parts. Key elements to consider when selecting seals and gaskets are outside diameter, inside diameter, material, and whether the operation involves high heat.