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How to Measure Miniature Bearings

Miniature bearings allow rotation of a wheel on a rotating shaft fluidly without friction. Miniature bearings are used in remote control cars and trucks, skates of all types and skateboards. The balls inside the race of a bearing need lubrication to allow the wheel to spin correctly. Non-lubricated bearings do not allow the balls to spin and the wheel locks up. Measuring your faulty miniature bearings allow you to correctly obtain a replacement in the same size.

Things You'll Need

Digital calipers

Instructions

- 1
  Press the "On" button on a pair of digital calipers to turn the calipers on. Press the "On/Inch/mm" button to change the unit of measure to "mm" if it is currently displaying inches.
- 2
  Place the two small jaws on top of the digital calipers inside the bearing race. This area is the hole in the center of the bearings where they mount to an object. Slide the jaws open until they touch the inner sides of the race. Read the measurement on the calipers display screen. This is the inside diameter, or bore, of the bearing.
- 3
  Push the "Zero" button to clear the display. Open the two large jaws and insert the bearing into the jaws with the hole in the center facing up. Push the jaws closed until they touch the sides of the bearing race. Read the display for the outside diameter of the bearing.
- 4
  Clear the calipers display. Turn the bearing over 90-degrees. Open the large jaws and insert the bearing. Close the jaws until they touch the top and bottom of the race. The hole in the center of the race is covered by the two jaws. Read the display for the width of the bearing.
- 5
  Order or purchase a new bearing by the bore size first, the diameter second and the width last. For example, a 3 by 8 by 4 miniature bearing has a bore of 3 mm, an outside diameter of 8 mm and a width of 4 mm.

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