A bearing is a machine part which

A bearing is a machine part which supports a moving element and confines its motion. The most important as well as the most common aplications of bearings are those in which the relative motion between the members is either a sliding action guided in a straight line as between a planer table and its bed; or the motion is rotation, as in the case of a shaft with its axis held in a fixed position by journal bearings, and endwise movement prevented by thrust bearings. A journal bearing is one which forms a sleeve around a shaft and supports a load at right angles to the shaft axis. The journal is that part of the shaft which rotates in the bearing. A thrust bearing is one which takes a thrust load in the direction of the axis of the shaft. When worn, the bearing may be restored to its original condition by replacing the liner. The piston pin bearing in an automobile connecting rod is a familiar example of this type of bearing. For ordinary work, light loads, and moderate speeds, unlined cast-iron bearings may be used.