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.
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.
R-series and 1600-series ball bearing dimensions
Use a complete model marking first, then compare bore d, outside diameter D and the correct width W. The original inch decimals and their millimetre conversions are shown together; this is a reference table, not a list of approved substitutes.
55 matching base models. Filters update as you type when JavaScript is enabled.
On small screens, scroll each table sideways. “Not separately listed” means this source does not establish that configuration; it does not mean zero width or unavailable.
1600 series: base width and explicit sealed-width exceptions
| Base model | Bore d | Outside D | Base width W | Sealed width (footnote) | Radius r (in) | Dynamic C (lbf) | Static C0 (lbf) |
|---|---|---|---|---|---|---|---|
| 1601 | 0.1875 in4.7625 mm converted | 0.6875 in17.4625 mm converted | 0.2500 in6.35 mm converted | 0.3125 in7.9375 mm converted | 0.011 | 440 | 170 |
| 1602 | 0.2500 in6.35 mm converted | 0.6875 in17.4625 mm converted | 0.2500 in6.35 mm converted | 0.3125 in7.9375 mm converted | 0.011 | 440 | 170 |
| 1603 | 0.3125 in7.9375 mm converted | 0.875 in22.225 mm converted | 0.2812 in7.14248 mm converted | 0.34375 in8.73125 mm converted | 0.011 | 740 | 310 |
| 1604 | 0.3750 in9.525 mm converted | 0.875 in22.225 mm converted | 0.2812 in7.14248 mm converted | 0.34375 in8.73125 mm converted | 0.011 | 750 | 320 |
| 1605 | 0.3125 in7.9375 mm converted | 0.9062 in23.01748 mm converted | 0.3125 in7.9375 mm converted | Not separately listed | 0.011 | 740 | 310 |
| 1606 | 0.3750 in9.525 mm converted | 0.9062 in23.01748 mm converted | 0.3125 in7.9375 mm converted | Not separately listed | 0.011 | 750 | 320 |
| 1607 | 0.4375 in11.1125 mm converted | 0.9062 in23.01748 mm converted | 0.3125 in7.9375 mm converted | Not separately listed | 0.011 | 610 | 290 |
| 1614 | 0.3750 in9.525 mm converted | 1.125 in28.575 mm converted | 0.3750 in9.525 mm converted | Not separately listed | 0.023 | 1150 | 540 |
| 1615 | 0.4375 in11.1125 mm converted | 1.125 in28.575 mm converted | 0.3750 in9.525 mm converted | Not separately listed | 0.023 | 1150 | 540 |
| 1616 | 0.5000 in12.7 mm converted | 1.125 in28.575 mm converted | 0.3750 in9.525 mm converted | Not separately listed | 0.023 | 1150 | 540 |
| 1620 | 0.4375 in11.1125 mm converted | 1.375 in34.925 mm converted | 0.4375 in11.1125 mm converted | Not separately listed | 0.023 | 1720 | 840 |
| 1621 | 0.5000 in12.7 mm converted | 1.375 in34.925 mm converted | 0.4375 in11.1125 mm converted | Not separately listed | 0.023 | 1720 | 840 |
| 1622 | 0.5625 in14.2875 mm converted | 1.375 in34.925 mm converted | 0.4375 in11.1125 mm converted | Not separately listed | 0.023 | 1720 | 840 |
| 1623 | 0.6250 in15.875 mm converted | 1.375 in34.925 mm converted | 0.4375 in11.1125 mm converted | Not separately listed | 0.023 | 1720 | 840 |
| 1628 | 0.6250 in15.875 mm converted | 1.625 in41.275 mm converted | 0.5000 in12.7 mm converted | Not separately listed | 0.023 | 2100 | 1110 |
| 1630 | 0.7500 in19.05 mm converted | 1.625 in41.275 mm converted | 0.5000 in12.7 mm converted | Not separately listed | 0.023 | 2110 | 1140 |
| 1633 | 0.6250 in15.875 mm converted | 1.75 in44.45 mm converted | 0.5000 in12.7 mm converted | Not separately listed | 0.025 | 3060 | 1480 |
| 1635 | 0.7500 in19.05 mm converted | 1.75 in44.45 mm converted | 0.5000 in12.7 mm converted | Not separately listed | 0.023 | 3060 | 1480 |
| 1638 | 0.7500 in19.05 mm converted | 2 in50.8 mm converted | 0.5625 in14.2875 mm converted | Not separately listed | 0.039 | 2890 | 1500 |
| 1640 | 0.8750 in22.225 mm converted | 2 in50.8 mm converted | 0.5625 in14.2875 mm converted | Not separately listed | 0.039 | 2260 | 1330 |
| 1641 | 1.0000 in25.4 mm converted | 2 in50.8 mm converted | 0.5625 in14.2875 mm converted | Not separately listed | 0.039 | 2410 | 1460 |
| 1652 | 1.1250 in28.575 mm converted | 2.5 in63.5 mm converted | 0.6250 in15.875 mm converted | Not separately listed | 0.043 | 4380 | 2560 |
| 1654 | 1.2500 in31.75 mm converted | 2.5 in63.5 mm converted | 0.6250 in15.875 mm converted | Not separately listed | 0.043 | 3650 | 2330 |
| 1657 | 1.2500 in31.75 mm converted | 2.5625 in65.0875 mm converted | 0.6875 in17.4625 mm converted | Not separately listed | 0.043 | 4380 | 2560 |
| 1658 | 1.3125 in33.3375 mm converted | 2.5625 in65.0875 mm converted | 0.6875 in17.4625 mm converted | Not separately listed | 0.035 | 4380 | 2560 |
R series: open versus shielded width
| Base model | Bore d | Outside D | Open width W | Shielded width W | Radius r (in) | Dynamic C (lbf) | Static C0 (lbf) |
|---|---|---|---|---|---|---|---|
| R09 | 0.0400 in1.016 mm converted | 0.125 in3.175 mm converted | 0.0469 in1.19126 mm converted | Not separately listed | 0.004 | 22 | 6 |
| R0 | 0.0469 in1.19126 mm converted | 0.1562 in3.96748 mm converted | 0.0625 in1.5875 mm converted | 0.0937 in2.37998 mm converted | 0.004 | 36 | 10 |
| R1 | 0.0550 in1.397 mm converted | 0.1875 in4.7625 mm converted | 0.0781 in1.98374 mm converted | 0.1094 in2.77876 mm converted | 0.004 | 42 | 13 |
| R1-4 | 0.0781 in1.98374 mm converted | 0.25 in6.35 mm converted | 0.0937 in2.37998 mm converted | 0.1406 in3.57124 mm converted | 0.004 | 63 | 20 |
| R133 | 0.0937 in2.37998 mm converted | 0.1875 in4.7625 mm converted | 0.0625 in1.5875 mm converted | 0.0937 in2.37998 mm converted | 0.004 | 28 | 10 |
| R1-5 | 0.0937 in2.37998 mm converted | 0.3125 in7.9375 mm converted | 0.1094 in2.77876 mm converted | 0.1406 in3.57124 mm converted | 0.006 | 96 | 34 |
| R144 | 0.1250 in3.175 mm converted | 0.25 in6.35 mm converted | 0.0937 in2.37998 mm converted | 0.1094 in2.77876 mm converted | 0.004 | 64 | 22 |
| R2-5 | 0.1250 in3.175 mm converted | 0.3125 in7.9375 mm converted | 0.1094 in2.77876 mm converted | 0.1406 in3.57124 mm converted | 0.004 | 126 | 40 |
| R2-6 | 0.1250 in3.175 mm converted | 0.375 in9.525 mm converted | 0.1094 in2.77876 mm converted | 0.1406 in3.57124 mm converted | 0.006 | 144 | 50 |
| R2 | 0.1250 in3.175 mm converted | 0.375 in9.525 mm converted | 0.1562 in3.96748 mm converted | 0.1562 in3.96748 mm converted | 0.012 | 144 | 50 |
| R2A | 0.1250 in3.175 mm converted | 0.5 in12.7 mm converted | 0.1719 in4.36626 mm converted | 0.1719 in4.36626 mm converted | 0.012 | 258 | 89 |
| R155 | 0.1562 in3.96748 mm converted | 0.3125 in7.9375 mm converted | 0.1094 in2.77876 mm converted | 0.125 in3.175 mm converted | 0.004 | 76 | 30 |
| R156 | 0.1875 in4.7625 mm converted | 0.3125 in7.9375 mm converted | 0.1094 in2.77876 mm converted | 0.125 in3.175 mm converted | 0.004 | 89 | 32 |
| R166 | 0.1875 in4.7625 mm converted | 0.375 in9.525 mm converted | 0.1250 in3.175 mm converted | 0.125 in3.175 mm converted | 0.004 | 160 | 60 |
| R3 | 0.1875 in4.7625 mm converted | 0.5 in12.7 mm converted | 0.1562 in3.96748 mm converted | 0.196 in4.9784 mm converted | 0.012 | 295 | 110 |
| R3A | 0.1875 in4.7625 mm converted | 0.5 in12.7 mm converted | 0.1960 in4.9784 mm converted | 0.196 in4.9784 mm converted | 0.012 | 295 | 110 |
| R168 | 0.2500 in6.35 mm converted | 0.375 in9.525 mm converted | 0.1250 in3.175 mm converted | 0.125 in3.175 mm converted | 0.004 | 60 | 31 |
| R188 | 0.2500 in6.35 mm converted | 0.5 in12.7 mm converted | 0.1250 in3.175 mm converted | 0.1875 in4.7625 mm converted | 0.006 | 186 | 84 |
| R4 | 0.2500 in6.35 mm converted | 0.625 in15.875 mm converted | 0.1960 in4.9784 mm converted | 0.196 in4.9784 mm converted | 0.012 | 335 | 139 |
| R4A | 0.2500 in6.35 mm converted | 0.75 in19.05 mm converted | 0.2188 in5.55752 mm converted | 0.2812 in7.14248 mm converted | 0.016 | 525 | 199 |
| R6 | 0.3750 in9.525 mm converted | 0.875 in22.225 mm converted | 0.2188 in5.55752 mm converted | 0.2812 in7.14248 mm converted | 0.016 | 745 | 315 |
| R8 | 0.5000 in12.7 mm converted | 1.125 in28.575 mm converted | 0.2500 in6.35 mm converted | 0.3125 in7.9375 mm converted | 0.016 | 1148 | 535 |
| R10 | 0.6250 in15.875 mm converted | 1.375 in34.925 mm converted | 0.2812 in7.14248 mm converted | 0.3438 in8.73252 mm converted | 0.031 | 1347 | 734 |
| R12 | 0.7500 in19.05 mm converted | 1.625 in41.275 mm converted | 0.3125 in7.9375 mm converted | 0.4375 in11.1125 mm converted | 0.031 | 1770 | 1018 |
| R14 | 0.8750 in22.225 mm converted | 1.875 in47.625 mm converted | 0.3750 in9.525 mm converted | 0.5 in12.7 mm converted | 0.031 | 2261 | 1316 |
| R16 | 1.0000 in25.4 mm converted | 2 in50.8 mm converted | 0.3750 in9.525 mm converted | 0.5 in12.7 mm converted | 0.031 | 2261 | 1316 |
| R18 | 1.1250 in28.575 mm converted | 2.125 in53.975 mm converted | 0.3750 in9.525 mm converted | 0.5 in12.7 mm converted | 0.031 | 2150 | 1407 |
| R20 | 1.2500 in31.75 mm converted | 2.25 in57.15 mm converted | 0.3750 in9.525 mm converted | 0.5 in12.7 mm converted | 0.031 | 2973 | 1858 |
| R22 | 1.3750 in34.925 mm converted | 2.5 in63.5 mm converted | 0.4375 in11.1125 mm converted | 0.5625 in14.2875 mm converted | 0.031 | 2756 | 1910 |
| R24 | 1.5000 in38.1 mm converted | 2.625 in66.675 mm converted | 0.4375 in11.1125 mm converted | 0.5626 in14.29004 mm converted | 0.031 | 2906 | 2084 |
Read the width and brand limits before comparing
- R-series W values distinguish open and shielded construction. Do not use a shielded value as a verified rubber-sealed value.
- For RBI 1601/1602 the sealed-width footnote is 5/16 in; for 1603/1604 it is 11/32 in. Other sealed widths are not separately established by this source.
- Millimetres here are arithmetic conversions of the published inch decimals, not manufacturer tolerance limits or extra measurement precision.
- These are RBI base-series references, not verified SKF, NICE/RBC or equipment replacements. Keep the full brand, suffix, clearance and mounting requirements.
- C and C0 are catalogue load ratings, not a permitted working load. No unlisted speed, vehicle fitment or lubrication recommendation is inferred.
- Flange dimensions and extended-inner-ring Wi values are deliberately outside this table; use the correct configuration drawing before comparing either feature.
Source: RBI Bearing Ball Bearings catalogue, printed pages 5–6, cross-checked against RBI public series tables; reviewed 2026-10-03. 1622: the PDF omits the width decimal; its 7/16 in fraction and the HTML entry both establish 0.4375 in. R24 shield width remains 0.5626 in as published. Independently organised by BearingScope.
What does your bearing size refer to?
A search such as 8 mm bearing or 1 inch ball bearing is not a complete part specification. Choose the measured feature below: a shaft opening, an outside ring, an axial dimension or a loose sphere. The same number can lead to different results.
Results update immediately when a valid input changes. Changing the unit reinterprets the entered number: 1 inch means 25.4 mm. Unknown dimensions stay unknown. No bearing is selected until you choose the measured feature.
Enter a measurement and select its meaning to see a supported lookup.
Record a loose-ball specification, not a bearing bore
mm is the requested sphere diameter. Also retain material, ball grade, gauge or diameter deviation, lot requirements and quantity. A grade is not a nominal size or an assembled-bearing ABEC class.
This tool does not list a loose ball as an available product, infer the ball count inside a bearing, or approve replacing rolling elements. A nearby metric or inch size is not automatically interchangeable.
Match the other dimensions, the complete suffix and the drawing before comparison. Width labels B and assembly height T are retained separately. Nominal size alone does not approve a fit or replacement.
| Brand / model | Original construction | Bore d | Outside D | Axial dimension | Closure |
|---|
No record matches these conditions in this reviewed snapshot. Remove a condition or inspect the broader catalogue. No nearby size is substituted.
Open broader catalogue search for this measurement → The broader catalogue can contain components outside this verified complete-bearing snapshot.
Common measurements from the keyword library
These are requested measurements, not a claim that every size is manufactured. Counts below belong to the 29,253-record reviewed snapshot, across its ball and roller bearing structures. Choose the measured feature after opening a size.
Before calling a size a match
- For a complete bearing, keep all measured dimensions and the complete marking. One size produces candidates, not a replacement approval.
- A loose ball has one diameter. Do not treat a steel-ball diameter as a shaft opening or infer internal ball dimensions from d×D×B.
- Enter fractions explicitly. “1 2 inch” could be a lost fraction or two numbers; the tool will not silently convert it to 1/2 or 12.
- This snapshot excludes separate cups/cones, housings, matched sets and needle roller sets without an inner ring. Use the appropriate component drawing for those parts.
Technical basis: JTEKT boundary-dimension definitions; NIST exact inch-to-millimetre relationship; the existing precision-ball specification guide. Product values retain the reviewed manufacturer-property snapshot dated 2026-10-02. This page is a research aid, not stock availability, a toleranced drawing or installation approval.
Bearing inch fractions to millimetres
Multiply inches by exactly 25.4 to obtain millimetres; divide millimetres by 25.4 for inches. The table converts lengths, not bearing model numbers. A converted length does not establish a manufactured size or a replacement.
| Inch fraction | Decimal inches | Millimetres |
|---|---|---|
| 1/16 in | 0.0625 in | 1.5875 mm |
| 3/32 in | 0.09375 in | 2.38125 mm |
| 1/8 in | 0.125 in | 3.175 mm |
| 5/32 in | 0.15625 in | 3.96875 mm |
| 3/16 in | 0.1875 in | 4.7625 mm |
| 1/4 in | 0.25 in | 6.35 mm |
| 5/16 in | 0.3125 in | 7.9375 mm |
| 3/8 in | 0.375 in | 9.525 mm |
| 7/16 in | 0.4375 in | 11.1125 mm |
| 1/2 in | 0.5 in | 12.7 mm |
| 9/16 in | 0.5625 in | 14.2875 mm |
| 5/8 in | 0.625 in | 15.875 mm |
| 11/16 in | 0.6875 in | 17.4625 mm |
| 3/4 in | 0.75 in | 19.05 mm |
| 7/8 in | 0.875 in | 22.225 mm |
| 1 in | 1 in | 25.4 mm |
| 9/8 in | 1.125 in | 28.575 mm |
| 5/4 in | 1.25 in | 31.75 mm |
| 3/2 in | 1.5 in | 38.1 mm |
| 7/4 in | 1.75 in | 44.45 mm |
| 2 in | 2 in | 50.8 mm |
| 5/2 in | 2.5 in | 63.5 mm |
| 3 in | 3 in | 76.2 mm |
Use a complete size, not just an inch bore
If an identified part is marked 1/2×1-1/8×5/16 inch, the corresponding length calculation is 12.7×28.575×7.9375 mm. This is an arithmetic example, not a claim that a particular bearing exists. Confirm all three dimensions and the complete part number against its source.
The size finder above accepts mixed fractions with spaces, such as 1 1/8. In a search phrase, “1 2 inch” might mean 1/2 inch or two unrelated numbers: check the original marking rather than silently guessing. A near metric match is not a fit approval.
Conversion basis: NIST SI Units — Length. Converted display values may be rounded; fit decisions require the original unit, tolerance and drawing.
Search source-labelled sizes in inches or mm →What to check
Enter fractions without losing precision
The size finder accepts 1/2 and mixed fractions such as 1 1/4 in inch mode. A 1/2 inch bore becomes 12.7 mm; it is not a 12 mm or 13 mm bore.
Keep all three dimensions
A matching bore does not identify an inch bearing. Convert outside diameter and assembly width as well, and retain the original designation and cup/cone numbers.
A metric designation is not an inch cross reference
A near-sized metric bearing can need a different shaft or housing. Use the original engineering drawing and fits, not a rounded conversion.
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
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.
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.