Selecting the correct bearing size is critical for performance and service life. Whether you're replacing an old bearing or designing new equipment, getting the size right is essential. This guide walks you through the process step by step.
If you're replacing an existing bearing, the easiest way to find the size is to check the markings on the bearing itself. Most bearings have the part number stamped or etched on the outer ring face.
Common markings include:
The bearing part number (which corresponds to specific dimensions)
The brand name
The ABEC precision grade (if applicable)
Once you have the part number, you can look up the exact dimensions from a bearing catalog or directly order an equivalent replacement.
If the old bearing is unmarked or the markings are worn away, you'll need to measure the three key dimensions yourself. You need:
Bore diameter (d) – the inner diameter of the bearing (shaft diameter)
Outer diameter (D) – the outer diameter of the bearing
Width (B) – the thickness/width of the bearing
Use a micrometer or caliper for accurate measurements. Measure to at least one hundredth of a millimeter (0.01mm) accuracy.
Besides size, you also need to confirm which type of bearing you need:
Deep groove ball bearing – most common for general purpose use
Angular contact ball bearing – for combined radial and axial loads
Cylindrical roller bearing – for high radial loads
Spherical roller bearing – for heavy loads and misalignment
Tapered roller bearing – for combined radial and axial thrust loads
Needle roller bearing – for high radial loads in limited space
Size alone isn't enough – you need to make sure the bearing can handle the loads in your application. Calculate the expected radial and axial loads, then choose a bearing with a dynamic load rating (Cr) that exceeds your calculated maximum load with an appropriate safety factor.
Factor in other operating conditions:
Operating temperature
Rotational speed
Lubrication requirements
Sealing needs (contamination/moisture)
Required precision/clearance
Here are some popular metric bearing sizes to give you an idea:
| Bore (mm) | Outer (mm) | Width (mm) | Common Deep Groove Part Number |
|---|---|---|---|
| 10 | 30 | 9 | 6200 |
| 12 | 32 | 10 | 6201 |
| 15 | 35 | 11 | 6202 |
| 17 | 40 | 12 | 6203 |
| 20 | 47 | 14 | 6204 |
| 25 | 52 | 15 | 6205 |
| 30 | 62 | 16 | 6206 |
| 35 | 72 | 17 | 6207 |
If you have a part number but can't find the original brand, or if you need help selecting the right bearing, MS Bearings can help. We supply equivalent bearings for virtually every common bearing size and type, with identical dimensions to the original.
Send us your part number or dimensions, and we'll quote you a high-quality equivalent at 30-50% less than the original brand price. Contact us today.
