Bearings Knowledge-how to measure a bearing

STEP 1 Measuring the Bearing Bore (Inner Diameter / ID)

The bearing bore size is the measurement of the hole in the center of the bearing.

• Best method: Use a vernier caliper for the most accurate result.

• Steps:

  1. Insert the outer anvils of the caliper into the bearing’s bore.

  2. Open the caliper slowly until it fits snugly but not tightly against the inner ring.

  3. Read the measurement on the caliper scale in millimeters or inches.

Pro tip: If a vernier caliper is not available, a high-quality steel ruler can be used for approximate measurements.

STEP 2 Measuring the Outside Diameter (OD)

The outside diameter is the total width across the bearing from one outer edge to the other.

• Place the jaws of the caliper around the outer ring of the bearing.

• Close the jaws gently until they make contact without compressing the bearing.

• Record the measurement in mm or inches.

This dimension is critical when fitting the bearing into a housing or casing.

STEP 3 Measuring the Bearing Width (W)

The width refers to the thickness of the bearing.

• Position the caliper jaws on both sides of the bearing’s faces.

• Close until snug, ensuring no extra pressure is applied.

• Read the value to determine the exact width.

Why Accurate Bearing Measurement Matters

Choosing the correct bearing dimensions ensures:

• Proper fit in mechanical assemblies

• Longer service life and reduced wear

• Smooth rotation and minimal vibration

For precise results, always use a vernier caliper and measure at least twice to confirm accuracy. This is especially important for miniature bearings and micro-sized bearings where tolerances are very tight.