Ball Bearing Size Chart: Find Your Exact Metric & Inch Specs

Nothing kills a project faster than a seized motor or a wobbly shaft caused by the wrong bearing. If you guess the dimensions, you’re just inviting a catastrophic mid-project breakdown that will cost you twice as much to fix later. This ball bearing size chart provides the exact metric and imperial specs it is requisite to avoid those headaches. Whether you’re dealing with a standard deep groove ball bearing or a specialized high-speed component, getting the bore, outer diameter, and width right is the difference between a smooth machine and a pile of scrap metal. You can save this PDF to your phone or print it out to tape right above your workbench.

Reading the Standard Bearing Size Chart

To use the table effectively, it demands recognize how manufacturers code their parts. Most bearings follow a standard ISO-based numbering system where the first few digits define the series—like the 6000 or 6200 series—and the final two digits indicate the bore diameter. For instance, a bearing ending in "05" typically denotes a 25mm bore. If the number ends in "04," you're looking at a 20mm bore. It’s a simple system, but miss one digit and you’ll end up with a component that won't seat in your housing.

Here’s the catch: the series number isn't just a label. A 6205 bearing is physically thicker and capable of handling higher radial loads than a 6005. If you swap a lighter series into a high-load application, the raceway will deform under pressure—leading to premature spalling and total failure. Always cross-reference your part number with the standard bearing dimensions to ensure your load capacity matches the task.

Decoding the Specs

• Bore Diameter: The inner circle that slides onto your shaft.
• Outer Diameter: The measurement that must be a press-fit into your housing.
• Width: The contact surface area; too thin, and you lose stability.

Before you commit to a purchase, grab a set of digital calipers. Measure the bore to the nearest 0.01mm. If your shaft reads 12.7mm, you aren't looking for a 12mm metric bearing—you're looking for a 1/2-inch imperial size. Ignoring that 0.7mm difference forces you to rethink the entire assembly, as a loose fit allows for vibration that will destroy your housing in hours.

Analyzing Dimensional Criticality: Metric vs. Imperial Specs

The provided chart serves as a technical baseline for identifying replacement components. But precision requires understanding the delta between these standards. Consider the 6204 series, which features a 20mm bore and a 47mm outer diameter (OD). A common field error involves confusing this with a 0.75-inch shaft (19.05mm). Attempting to mount a 20mm bore bearing onto a 19.05mm shaft results in a 0.95mm clearance gap; this creates an unacceptable radial play that will lead to catastrophic cage failure and housing fretting within minutes of operation.

Imperial "R" series bearings operate on a fractional logic that often conflicts with metric housings. For instance, the R8 bearing has a 0.5-inch (12.7mm) bore and a 1.125-inch (28.575mm) OD. If a technician attempts to seat an R8 into a housing designed for a 6001 metric bearing (which requires a 28mm OD), they'll encounter a 0.575mm interference deficit. This mismatch prevents proper press-fit seating, leading to "spinning" in the housing, which effectively destroys the tolerance of the assembly.

The Risks of Dimensional Overlap

In mechanical repair, a shared bore dimension often masks significant differences in load-bearing capacity. Take the 6202 and 6302 series: both share an identical 15mm bore. However, the 6202 has an OD of 35mm and a width of 11mm, while the 6302 steps up to a 42mm OD and a 13mm width. Swapping these based solely on the bore size is a frequent cause of premature failure; the 6302 is designed for higher radial loads, and its larger cross-section provides the necessary rigidity that the 6202 simply can't support.

• R2 Series (3.175mm / 0.125" bore): These ultra-small bearings are ubiquitous in high-RPM hobbyist gearboxes. Because their width is only 3.969mm, they're drastically sensitive to axial loading; applying any side-force during installation will deform the race immediately.
• 6000 Series (10mm bore / 26mm OD): These are often utilized in low-profile, light-duty applications. Their 8mm width makes them unsuitable for high-torque industrial drive shafts, where a wider series would be required to distribute the mechanical stress.
• R16 Series (25.4mm / 1" bore): Representing the heavy-duty end of the imperial spectrum, these units feature a 12.7mm width. They are engineered for significant load-bearing, and substituting a smaller R-series bearing in their place will lead to rapid fatigue of the rolling elements.

When your measurements fall between these data points—such as an OD of 34mm—it's a clear indicator that you're dealing with either a proprietary non-standard bearing or significant wear. Never attempt to "shim" the difference between a 34mm seat and a 34.925mm R10 series outer race. Shims create non-uniform contact patches, which concentrate stress on the outer ring and lead to immediate spalling. Always verify the series number against the chart and, when in doubt, use a digital micrometer to confirm the OD and width to the nearest hundredth of a millimeter before proceeding with a press-fit.

Pro Tips for Measuring and Selecting Bearings

Stop guessing. A loose fit forces you to account for vibration damage that will chew through your housing in under an hour. Always check for shields or seals—the "ZZ" suffix indicates metal shields for debris protection, while "2RS" denotes rubber seals for grease retention. If you're working on a high-speed motor, sticking with an open bearing will lead to instant lubricant leakage. You can download this chart as a PDF to keep on your garage wall. Print this out and keep it near your press.

Common Questions

• What if my size isn't on the chart? You likely have a proprietary part or an older machine standard; check the manufacturer's manual or consult an ISO bearing catalog for obscure series.
• Can I use a wider bearing to add stability? Only if your shaft length and housing clearance allow it—adding width without space causes the bearing to bind.
• Why is my bearing "clicking" after install? You probably over-tightened the press fit or introduced grit during installation; clean the seat and re-check your tolerance.
• Does the brand matter? Cheap bearings often use lower-grade steel that warps under heat; stick to reputable manufacturers for high-RPM tasks.
• How do I measure a worn bearing? Use digital calipers on the least-worn section of the raceway, but accept that you might need to test-fit a new one to confirm.

Save this guide for your next teardown. Having the right dimensions before you start saves you from a seized machine. Grab the printable version and keep this reference handy whenever you're at the bench.