How to measure a bearing?

To measure a bearing, the most appropiate tool is a pie de rey (spanish word) also called a caliper or micrometer but, failing that, a simple millimeter ruler (mm) can also be used.

We must find out 3 numerical values that are those that physically define the reference of a bearing and whose designation is recognized internationally in all catalogs and reference tables with the letters d x D x B being:

• d: inside diameter
• D: outside diameter
• B: width

MEASURE A BEARING WITH A CALIPER:

The caliper or Pie de Rey (in Spanish) is a measuring instrument that allows you to find out internal, external diameters and depths in both mm and inches.

How to measure the inside diameter of a bearing:

1. The mobile ruler slides this time with the upper caliper jaws that are inserted between the bearing walls until it reaches the stop.
2. We block the measurement by screwing the fixing screw
3. We read the measurement in mm in the lower part of the moving ruler.

How to measure the outer diameter of a bearing:

1. The mobile ruler is slid to open it until the bearing is caught between the two lower calipers or jaws that make contact with the bearing.
2. We block the measurement by screwing the fixing screw
3. We read the measurement in mm in the lower part of the moving ruler.

How to measure the width of a bearing:

We perform the same operation as with the outside diameter, using the lower caliper jaws.

Measure a bearing with a millimeter ruler:

If you have to proceed with a millimeter rule, the process will not be as precise but it will be equally valid.

FOR WHAT ARE THE MEASURES OF A BEARING?

After disassembling our skate, skate or bicycle we can find in the hand with a bearing that we have decided to replace but whose reference or standard designation does not appear anywhere. Wear, dirt or poor condition of the bearing can make such information illegible. 

That is when we have to turn to a specialized mechanic or find out what the dimensions of our bearing are in order to buy it.

These measures are the basic information to proceed with the identification of the bearing and then we will find a wide variety of types and versions of bearings, suitable for each application: speed or artistic skating, MTB or road bike, skate …

There are also other types of measures that are essential in the selection of some types of bearings such as the degrees of the angle of the chamfers in the Steering Bearings of the bicycle. In this case, the measurements are usually printed on the bearing ring and the first number that refers to the inner angle and the second to the outer angle.