Bearing speed is one of the most important factors influencing the temperature rise of a bearing. The maximum permissible speed of the bearing, i.e. the limiting speed, decreases as the diameter series and width series of the bearing increase. Bearing samples or design manuals include various types and sizes of bearing limit speed nlim values, whose test conditions are equivalent dynamic load P<=0.1C (C is the basic rated dynamic load), normal cooling conditions, and the maximum permissible speed for a 0-level tolerance bearing. However, as the limiting speed is mainly limited by the temperature rise during operation, the limiting speed in the sample cannot be considered to be an absolute limit that cannot be exceeded. For each bearing, there is its own limit speed. The speed of the bearing is mainly limited by the temperature rise caused by the frictional heat inside the bearing, when the speed exceeds a certain limit, the bearing will not be able to continue to rotate due to burns, etc., or even make the bearing seized. Therefore we are rotating the right type of bearing according to the speed of the bearing, then we need to go to understand what are the requirements of the speed selection bearing. In some applications, other factors are more important than the limiting speed. For example: low speed, reciprocating oscillation, etc. The limiting speed of a bearing is the limit value at which frictional heating leading to burns does not occur and continuous rotation is possible. The limiting speed of a bearing therefore depends on various factors such as the type, size and accuracy of the bearing as well as the type of lubrication, the quality and quantity of the lubricant, the material and type of cage and the load conditions. The limit speed given by the bearing manufacturer generally refers to the highest speed that can be achieved under the agreed conditions: for example, the bearing tolerance is 0 level; the bearing clearance is 0 group; the bearing load is 10% of the rated load; the lubrication and cooling conditions are normal; the radial bearing only bears radial load, the thrust bearing only bears axial load; the outer ring temperature does not exceed 100℃, etc. The speed range required by the use of the occasion helps to decide what type of bearing to use. Most bearing manufacturers’ catalogues provide limit speed values for their products, and practice has shown that it is better to work at less than 90% of the limit speed.