What are the methods for measuring bearings?
1. Outer Diameter Measurement: The outer diameter of the bearing is measured using a micrometer or outside gauge. This method is commonly used for bearings with a large outer diameter and short length.
2. Inner Diameter Measurement: The inner diameter of the bearing is measured using a caliper or vernier caliper. This method is commonly used for bearings with a large inner diameter. Additionally, the bearing bore can be measured using an inside diameter gauge after verifying the reference dimension on an outside micrometer. The roundness and cylindricity of the bearing bore also need to be measured.
3. Wall Thickness Measurement: The wall thickness of the bearing is measured using a micrometer or outside gauge. This method is commonly used for bearings with thinner walls.
4. Vibration Spectrum Analysis: By measuring the vibration acceleration, velocity, and displacement values of the bearing at different frequencies, its spectral characteristics are analyzed to determine the bearing's operating condition. This method requires high-precision vibration sensors and a spectrum analyzer, offering high accuracy, but the measurement time is relatively long. 
5. Impact Pulse Method: This method measures the impact pulse signals generated by the bearing during operation, analyzes the pulse amplitude and frequency characteristics to determine the degree of bearing damage. It is fast and simple, but its accuracy is slightly lower than the vibration spectrum analysis method.
6. Temperature Measurement Method: This method measures the bearing's operating temperature and analyzes its temperature change trends to determine the bearing's operating condition. This method is simple and easy to implement, but for high-speed bearings, temperature changes are small, resulting in lower accuracy.
In addition, there are methods such as rotational testing, noise testing, friction testing, and life testing to comprehensively evaluate the bearing's performance and condition. Rotational testing checks the bearing's rotational stability, noise testing checks the sound during bearing operation, friction testing assesses the magnitude of friction during bearing rotation, and life testing assesses the bearing's service life under specified conditions.