Clearance is an important performance parameter of bearings. Bearings with different clearances are used in different mechanical operating conditions. In the bearing configuration of motors, different manufacturers will adopt different designs, mainly based on the processing quality of parts and components and the relevant tolerance range; in the era of unified motor design, the tolerances of all parts are the same, so the initial quality supervision and spot check of the whole machine is to detect the size of parts. With the control of motor product quality and performance results, different motor manufacturers have relatively large freedom in the design of parts, whether it is the structure of parts or the corresponding tolerance range; some high-quality motor products naturally incorporate relatively high-quality parts and more reasonable tolerance matching. In terms of the selection of motor bearings, some manufacturers uniformly adopt the basic group of radial clearance as the bearing configuration rule for all motors, and some uniformly choose C3 clearance bearings, while some motor manufacturers configure bearings with different radial clearances according to different pole numbers, such as 2, 4, 6, 8-pole motors choose C3 clearance bearings, while motors with 10 poles or more choose the basic group clearance, thereby better ensuring the mechanical performance level and noise and vibration performance requirements of the motor.