In the modern world, there are two types of bearings. They are the plain (sliding) and rolling element bearings. Bearings are machine elements that permit directed relative motion between two parts. Forces are transmitted from one part to another without allowing motion in direction of the applied load. A journal bearing consists of an approximately cylindrical body around a rotating shaft. This journal bearing is used either for supporting a radial load, or simply as a guide for smooth transmission of torque. Most common applications of bearings are the plain circular bearings type. Lubrication usage, on the other hand, range from a simple inlet hole to axial, circumferential, and helical grooves for efficient lubrication distribution.

The plain bearing applications include reciprocating sliders, rotating or oscillating cylindrical members sliding in annular sleeves, and rotating or rotationally oscillating disks sliding on mating disks. The advantages of plain bearings are as follows: lower first cost, simple design, small radial space required, quiet operation, not so sensitive to dust or grit, less likely to be subjected to fatigue failure, easy to replace,. Material types for the plain bearing should have the following: adequate compressive strength, good fatigue strength, low elastic modulus, good ductility and low hardness, high thermal conductivity and compatible thermal expansion coefficients. The shaft must be made from low or medium steel or steel alloys. For the bearing element, bronze bearing metal, ‘babbit’ or ‘non’ metallic materials are used.