Measure the total diameter of the ball bearing in millimeters, as viewed from its circular side. Diameter measure the width of a circle along a line that passes through its center. (See Reference 2)
2
Determine the diameter, in millimeters, of the central hole in the bearing. This will ensure the replacement bearing fits onto its shaft.
3
Measure the thickness of the bearing as viewed from its edge in millimeters. You now have all relevant dimensions of the ball bearing.