How to Read a Bearing Size Chart + Free Dimension Reference Tables

Standards Note

Bearing size charts standardize physical dimensions across brands under ISO 492 (radial bearings) and ISO 355 (tapered roller bearings). A bearing number, a measured bore, and a housing diameter together give you everything you need to select or verify a bearing without opening a full catalogue.

Bore Diameter (d)

The bore is the inner hole that slides onto the shaft. It is always the starting point.

• ID (inner diameter) — also written this way
• Must match shaft diameter with the correct tolerance class — not approximately, exactly
• A 0.02 mm difference between a k5 and an m5 shaft fit determines whether the inner ring rotates with the shaft or on it

Outer Diameter (D)

The OD is the outside surface that seats into the housing.

• Must match the housing bore with the correct fit class
• Too loose: outer ring spins in the housing, wears the seat, generates heat
• Too tight: outer ring distorts, changes internal clearance, accelerates fatigue

Width (B or T)

Width is the axial thickness of the assembled bearing. Thrust bearings use T instead of B.

• Determines axial space occupied in the assembly
• Sealed bearings (2RS) often run 0.5–1 mm wider than open bearings of the same part number — always check the sealed spec separately
• Width alone does not determine load capacity; that comes from the dimension series

Format (6×00 series):

[Type][Series][Bore Code][Suffix]

This format applies to 6×00-series deep groove ball bearings. NU-series, 22-series, and 32-series bearings follow variant prefix conventions — check the relevant series catalogue for those.

Common Misunderstanding: C3

C3 is not a premium grade. It is a bearing with deliberately more internal play — designed for applications where the inner ring expands onto the shaft under heat or press fit. In a standard room-temperature application with a normal shaft tolerance, C3 gives you more looseness than the position actually needs. That extra play increases noise and cuts fatigue life.

Find or recover the part number

Check the outer ring of the existing bearing. The designation is stamped or laser-engraved on the ring face. Write it down in full, including any suffixes — a bearing marked 6205 and one marked 6205-2RS/C3 are different products.

If the number is worn or corroded, measure bore, OD, and width with digital calipers and locate the bearing by dimension in the reference tables below. You can also use our Bearing Cross Reference tool to match across brands. If you need a replacement 6205 or similar, our bearing catalogue lists full specifications and availability.

Locate the correct series section

Charts organize by series — all 6200-series bearings together, all 6300-series together. Find the right section before scanning rows. Jumping straight to scanning without knowing the series wastes time and risks landing on the wrong row.

If you only have dimensions and no part number, start with bore to narrow the series, then match OD to confirm.

Read and verify the three core dimensions

All three must match. One mismatch means the bearing will not fit or will fail early from incorrect fit pressure.

Check load ratings for new selection

For direct like-for-like replacement, skip this step — the original part number already tells you what load level this position requires.

For a new selection or series change:

• C (kN) — Dynamic load rating. Higher C means longer calculated life under the same rotating load. The relationship is cubic: doubling the applied load cuts L10 life to one-eighth.
• C₀ (kN) — Static load rating. Use this for stationary loads or slow oscillating movement. Never apply a load exceeding C₀.

For the full calculation method including the ISO 281 L10 formula, use our Bearing Life Calculator.

Check the speed limit

Every chart row includes a maximum RPM under grease lubrication. Confirm your application speed sits below this number.

Sealed bearings (2RS) have a lower speed limit than the equivalent open bearing — check the sealed variant's own row in the chart for the exact figure rather than assuming it matches the open spec.

Key Takeaway

Reading a bearing size chart correctly means verifying all five data points: bore (shaft match), OD (housing match), width (axial space), load rating C or C₀ (application load), and maximum RPM (application speed). Missing any one is where most replacement errors start.

Mistake 1: Reading bore code as bore size

Bore code 05 is not 5 mm. It is 25 mm (05 × 5). This error appears on ordering forms more often than you would expect — usually when someone copies the bore code column instead of the bore dimension column when transcribing from the chart.

Mistake 2: Ordering an inch bearing to replace a metric one

Both might look close in bore size. But "close" fails. An R10 bearing has a 5/8″ (15.875 mm) bore — not 15 mm, not 16 mm. In a housing bored for a metric 15 mm bearing, that difference means it either does not fit or spins loose. Always confirm the measurement system your equipment uses before placing an order.

Mistake 3: Assuming sealed bearings match open bearing widths

A sealed 6205-2RS runs approximately 0.5 mm wider than an open 6205 in most manufacturer specs. In a tight motor end plate, that half millimeter binds the shaft. We have seen this cause shaft seizure in applications that ran fine for years until someone swapped in a sealed replacement. Always check the sealed variant's own dimension row.

Mistake 4: Misreading the speed limit column

Many charts list a single RPM figure. That number applies to the open bearing. A sealed version of the same bearing has its own, lower speed limit listed in a separate row. We have seen motors overheat within days of a sealed bearing swap, and the first thing we checked was whether the sealed speed limit had been compared against actual shaft speed. It had not. If your application runs anywhere near the listed RPM, pull the sealed bearing's specific row and verify the figure directly.

Inner ring creep (shaft fretting): Check bore (d). If the shaft is worn undersize, the inner ring loses its interference fit and rotates on the shaft rather than with it.

Outer ring spin (housing fretting): Check OD (D). An oversized housing lets the outer ring spin — visible as fretting corrosion on the OD surface and a worn housing bore.

Axial binding or excessive end-float: Check width (B or T). The wrong width causes either preloading — which generates heat and shortens life — or excessive axial play, which shows up as noise and reduced positional precision.

Premature fatigue: Check C against actual load. L10 life scales with the cube of the load-to-rating ratio. A bearing running at twice its rated load has one-eighth the expected service life. Our Bearing Life Calculator handles this calculation directly.

What is the difference between C and C₀?

C is the dynamic load rating — the constant load under which the bearing achieves an L10 life of one million revolutions, as defined in ISO 281. C₀ is the static load rating — the maximum load the bearing can carry without permanent deformation when stationary. Use C when the shaft is rotating; use C₀ when the bearing supports a load while stationary or moving very slowly.

Why does a thrust bearing show a much higher C₀ than C?

Thrust ball bearings are designed primarily to resist permanent deformation under heavy axial loads, not to endure millions of rotational cycles. Their geometry makes them very stiff against static axial force but less efficient under dynamic rotating loads. The high C₀ relative to C is a deliberate design characteristic — not an error in the chart.

Can I search by dimension instead of part number?

Yes. Measure bore, OD, and width, then scan the d, D, and B columns in the relevant series table. If all three match a single row, that is your bearing. The Bearing Cross Reference tool also cross-references part numbers across brands if you have a competitor number to match.

Where can I download a complete bearing catalogue?

Catalogue sections covering over 25,000 bearing types are available on our catalogue download page.