How to Measure a Bearing: Bore, OD and Width

The three measurements

Almost every standard rolling bearing is identified by three dimensions, all in millimetres:

1. Bore — the inside diameter (the hole the shaft passes through).
2. Outer diameter (OD) — the diameter of the outside ring.
3. Width — the total thickness of the bearing.

What you need

A digital vernier caliper measuring to 0.1 mm is sufficient. Measure in millimetres — imperial bearings exist but are rare in modern industrial equipment.

Step by step

1. Clean the bearing so dirt does not affect the reading.
2. Measure the bore across the inner opening at two points 90° apart and take the average.
3. Measure the outer diameter across the outside ring at two points 90° apart.
4. Measure the width across the two faces.
5. Note the seal type (2RS, ZZ or open) and the brand if visible.

Reading the part number

For a standard deep groove ball bearing the last two digits of the part number multiplied by 5 give the bore — a 6205 has a 25 mm bore. The full bore × OD × width set confirms the exact variant. If the number is unreadable, the three measurements plus the seal type are enough for our team to identify it.

Tips

• Worn bearings may measure slightly under nominal; round to the nearest standard size.
• Taper and roller bearings need the same three measurements but may also need the taper angle — call us if unsure.
• If you have a competitor part number, use our cross-reference chart instead of measuring.