Identify a bearing using the bearing part number stamped or printed on one side of the bearing. If the part number is worn down from use, take measurements of the bearing to identify its type, size and use.
For a bearing without a part number, measure it using a micrometer. Calibrate the micrometer by fitting the gauge block between the tips and closing the micrometer so that the tips contact the block. Check that the margin of error is not more than plus or minus .0005. Measure the bearing's inside diameter by opening the micrometer to the size of the inside opening and adjusting it until each side makes contact with the inside opening. Write the measurement with a "d=" in front of it.
Measure the outside diameter of a cleaned bearing in the same way. Write the measurement with a "D=" before it. Measure the bearing's width, and write it with a "B/T" in front of it. These three numbers are used to identify the part number. Consult a bearing dealer or a dealer website to find an identical part.
The three types of bearing are ball bearings, roller bearings and needle bearings. Ball bearings are spheres that separate the races inside a bearing. A roller bearing is circular and operates in a similar way to a ball bearing. A needle bearing has rollers to prevent friction.