Hydrostatic bearings and hydrodynamic bearings are fluid film bearings that rely on a film of oil or air to create a clearance between the moving and stationary elements. They are different than basic bearings, machine components that reduce friction between supports in order to move loads. Typically, hydrostatic bearings and hydrodynamic bearings are used whenever one machine part comes in contact with another. Without bearings, machine parts would need to be constantly replaced from the wear of friction. The two primary types of bearings are antifriction bearings such as roller bearings and ball bearings, and plain bearings such as journal bearings and trust bearings. An antifriction bearing reduces friction by removing sliding between surfaces and replacing part contact with rolling components. A plain bearing uses a lubricant to reduce the friction between the sliding surfaces.