When you need to replace a bearing, it is luck if there is a visible part number engraved onto the bearing. If not, it's time to inspect the old bearing and measure the bore diameter and other main dimensions.
Generally, there are three main measurements to a rolling bearing.
- The bore diameter (inner diameter, ID)
- The outer diameter (OD)
- Width or height
When we know these dimensions and what structure the bearing is, we can find out the bearing.
While all three measurements are important, the bore diameter gets partucular attention as this figure is entirely dependent on the shaft size.
What is a bore diameter
2, Thrust bearing
Bore diameter, often called the inner diameter (ID), is the measurement of the bearing's internal diameter. It determines the bearing's inner hollow size, and crucial for its interaction with the shaft.
The last one or two code of basic designation of bearing indicate bore diameter. (Please refer to Bearing meaning for more details. For example:
The bore diameter of 6205 is 5 x 5 = 25 mm
For rolling bearings, inner rings are fixed on the shaft so that relative movement doesn't occur between fitting surfaces during operation or under load. Types of fits include tight, transition and loose fitting, which may be selected depending on whether or not there is interference.
- Loose Fit: The bore is slightly larger than the shaft, allowing easy assembly but potentially less stability.
- Transition fit: Bore and shaft sizes align perfectly, offering a balance in performance and fit.
- Tight Fit: The bore is slightly smaller than the shaft, ensuring a secure grip, ideal for high-load scenarios.
Bearing fits can be selected by recommended fits.
How to measure a bearing
When measuring a bearing, many people attempt to use a ruler. You can get the bore diameter, outside diameter, and width this way, but it is not very accurate. The best way to measure a bearing is by using digital vernier calipers, which are designed to gauge internal and external dimensions with far greater accuracy. Their readings are accurate to within ±0.02 mm.
How to measure the bore diameter of a bearing
- Turn your digital calipers on and zero the data reading in the closed position.
- Place the bearing onto the inner measurement side of the calipers, roll them out to as far as the bearing will allow.
- Read and note down the measurement displayed.
Please note that you should wiggle the calipers inside the bearing inner ring to make sure they sit across the widest part.
Repeat the process above to measure the outside diameter. This time, using the external measurement side of the capiper calculate the outer diameter of the bearing.
Using the external measurement side once more measure the width or height of the bearing.