Bearings clearance refers to the amount of movement when one side of the inner or outer ring of a bearing is fixed before it is mounted on an axle or bearing housing, and the other side is moved radially or axially. Depending on the direction of movement, it can be classified into radial clearance and axial clearance. The size of the clearance during operation (also known as working clearance) affects the bearing's performance, such as rolling fatigue life, temperature rise, noise, and vibration. To obtain a stable measurement value when measuring the bearing clearance, it is generally necessary to apply a specified measurement load. Therefore, the measured value is larger than the actual clearance (known as theoretical clearance) due to the elastic deformation caused by the measurement load. However, for roller bearings, this elastic deformation is relatively small and can be ignored. The internal clearance of the bearing before installation is usually represented by the theoretical clearance.