How to measure bearing bore, outside diameter & width
Record the component marking before measuring. The size finder expects bore d, outside diameter D and width B in that order, not the order in which the numbers happen to appear on a label.
On this page8 sections ⌄
Find by measured dimensions
Enter bore d, outside diameter D and width B. Use decimals or inch fractions such as 1/2 or 1 1/4.
Measure an unknown bearing for a catalogue search
For an ordinary radial bearing, record the shaft opening d, cylindrical outside D and axial width B. The sketch shows the measurement directions, not a toleranced drawing. A caliper can help identify a nominal catalogue size; it cannot certify the bearing tolerance class or a shaft fit.
- Save the identity. Photograph the complete marking, closures and both faces. Record whether you have a complete bearing, a separate ring, a mounted unit or a thrust assembly.
- Prepare the measurement. Isolate the machine before handling parts. Use clean accessible seating surfaces and check the instrument zero. Do not dismantle a sealed bearing merely to identify its size.
- Measure d and D separately. Check more than one angular position and plane. Note wear, damage or a tapered bore instead of averaging away the difference. For a formal accuracy check, follow the specified gauge method rather than a handheld approximation.
- Find the correct axial dimension. Use B for the specified radial ring width; a tapered cone/cup assembly needs T. A flange lip, extended ring or separate thrust washer can give a different reading.
- Record the units and all readings. Search the nominal candidate only after comparing the marking and measurement. For example, 1/2 inch is 12.7 mm; rounding it to 12 or 13 mm changes the requested part.
- Verify the candidate. Check the complete product drawing and component scope, then the load, speed, clearance, closures and fit requirements. Similar size is only an identification lead.
When three dimensions are not enough
| Observed feature | Extra information to retain | Do not assume |
|---|---|---|
| Flanged outer ring | Flange diameter and thickness, plus cylindrical D | Flange diameter is not automatically D |
| Tapered bearing | Both cone and cup numbers; assembly width T | Cone B plus cup C is not T |
| Needle bearing without inner ring | Roller-set bore Fw and shaft raceway requirements | A loose roller opening is not a ring bore d |
| Thrust bearing or mounted unit | Washer/height or complete housing interface drawing | A radial d×D×B table does not define its installation |
Reference basis: JTEKT boundary-dimension and tolerance-measurement guidance. This workflow is for identification, not acceptance inspection.
Use the source-labelled dimension chart →Measuring a needle bearing without rings?
Use the separate Fw / Ew / cage-width chart. It distinguishes ring bores from roller-complement diameters and keeps thrust-cage roller diameter separate from washer-inclusive height.
Open the source-labelled needle size chart →Looking up a thrust bearing by height?
Use the complete axial assembly chart to distinguish shaft and housing washer diameters, load directions and the envelope with a specified aligning seat washer.
Open the thrust bearing size query →What to check
Measure three different features
Measure the bore across an unworn seating surface, the cylindrical outer surface rather than a flange, and the correct ring or assembly width. Measure in more than one position. A worn part gives an estimate, not its original tolerance.
Recognize the exceptions
Tapered assemblies use total width T; thrust bearings use height; mounted units have mounting dimensions; flanged bearings need flange dimensions. Keep the drawing alongside your measurements.
Search, then verify
Use exact dimensions when the nominal size is known. If a worn measurement gives no match, use the catalogue minimum/maximum fields. Do not round an inch bearing into a nearby metric size.
Continue with real catalogue data
Preserve the full model, source description and unknown fields when making your shortlist. This reference website does not sell bearings or certify a replacement.
Related questions and tools
Inch bearing sizes, fractions & millimetre conversion
One inch is exactly 25.4 mm. Unit conversion changes the expression of a size, not its physical size or tolerance.
Read and apply →Bearing number decoder: series, bore codes & suffixes
A designation is a structured identifier, not a universal arithmetic formula. Read the complete prefix, basic number and suffix together.
Read and apply →Bearing dimension chart: sizes, brands & variants
This is a database-backed index, not a guessed standard-size list. Each model chart shows recorded dimensions and opens the actual products behind them.
Read and apply →Bearing weight & mass lookup
Bearing mass is a catalogue attribute. A solid-ring estimate cannot reproduce the mass of rings, rolling elements, cage and seals.
Read and apply →Reference basis & data limits
Manufacturer terminology is retained in the product records. Technical reference basis: JTEKT Basic Bearing Knowledge (boundary dimensions, tolerance classes and lubrication); NSK Bearing ABCs (lubrication, designations and clearance); NTN technical FAQs (closure codes and component interchange); SKF rolling-bearing selection and maintenance references.
Selection workflows and catalogue grouping are BearingScope editorial aids. Verify the current drawing and application requirements before using a candidate. Missing database information is not converted into an assumed match.