Precision bearing balls: sizes, grades, materials and loose-ball identification
A loose bearing ball is a spherical rolling element, not a complete ball bearing. Specify its ball diameter, material, precision grade and gauge or lot requirements. A size such as 1/4 inch does not identify the bore of a cartridge bearing, and a ball grade such as G10 is not an ABEC grade for an assembled bearing.
On this page17 sections ⌄
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.
Ball diameter is not bearing bore
In a complete bearing, d normally identifies the bore and D the outside-ring diameter. A loose ball has one nominal diameter. Searching '6 mm ball bearing' without specifying which of these you measured can therefore return completely different parts.
Use the size finder for complete bearings and retain the ball specification for loose-ball assemblies. Do not infer the ball count, pitch diameter or rolling-element diameter of a 608, 6204 or any other bearing from its external dimensions. Those internal values need an appropriate drawing or a direct source.
On smaller screens, scroll the table sideways to read all columns.
| Query describes | Record to keep | Do not infer |
|---|---|---|
| Loose ball | Nominal ball diameter, material, grade and gauge | A cartridge bearing number |
| Cartridge bearing | Brand, full marking, bore, outside diameter and width | Internal ball size or count |
| Bicycle cup-and-cone assembly | Exact hub specification, side, ball size and quantity | That all front or rear hubs share one ball size |
Fractional ball sizes converted to millimetres
Calculated from exactly 25.4 mm per inch. This is a nominal-size conversion table, not a stock list or a replacement recommendation. 1/4 inch is 6.35 mm, not 6 mm.
On smaller screens, scroll the table sideways to read all columns.
| Nominal diameter in inches | Nominal diameter in mm |
|---|---|
| 1/16 | 1.5875 |
| 3/32 | 2.38125 |
| 1/8 | 3.175 |
| 5/32 | 3.96875 |
| 3/16 | 4.7625 |
| 7/32 | 5.55625 |
| 1/4 | 6.35 |
| 5/16 | 7.9375 |
| 3/8 | 9.525 |
| 7/16 | 11.1125 |
| 1/2 | 12.7 |
| 5/8 | 15.875 |
| 3/4 | 19.05 |
| 1 | 25.4 |
| 1 1/2 | 38.1 |
| 2 | 50.8 |
| 3 | 76.2 |
| 6 | 152.4 |
What does a precision ball grade control?
A grade describes several properties, not just a plus/minus diameter tolerance. Selected values below are from Redhill Precision's published ISO 3290 reference table. Units are micrometres (µm); 1 µm = 0.001 mm. Obtain the current applicable specification and inspection certificate for acceptance testing.
Do not read G100 as a 100 µm tolerance or translate G10 to ABEC 10. Nominal diameter, grade and gauge address different parts of the specification. Mixing balls from different lots can defeat a tightly controlled assembly requirement even when the nominal size on the packets matches.
On smaller screens, scroll the table sideways to read all columns.
| Grade | Ball diameter variation (µm) | Deviation from spherical form (µm) | Surface roughness (µm) | Lot diameter variation (µm) |
|---|---|---|---|---|
| G3 | 0.08 | 0.08 | 0.010 | 0.13 |
| G5 | 0.13 | 0.13 | 0.014 | 0.25 |
| G10 | 0.25 | 0.25 | 0.020 | 0.5 |
| G20 | 0.5 | 0.5 | 0.032 | 1 |
| G100 | 2.5 | 2.5 | 0.100 | 5 |
Chrome steel, stainless steel and ceramic are not interchangeable labels
Precision-ball suppliers distinguish chrome steel, named stainless grades and ceramic materials. Abbott's precision-ball range illustrates the variety of material specifications used with ball grades. Material and precision must be recorded separately: a corrosion-resistant description does not establish diameter variation, surface finish or bearing suitability.
For a useful comparison, retain the exact material specification, hardness or heat-treatment requirement where specified, environment, lubricant and contact loading. Do not retrofit ceramic or stainless balls into an unidentified bearing by matching diameter alone.
Can I replace one missing ball with a same-size ball?
Only where the component's service instructions permit it and the full ball specification and quantity are known. Nominal diameter alone does not establish a matched set or restore damaged raceways.
Are lower ball-grade numbers more precise?
In the displayed grade system, smaller grade numbers correspond to tighter listed geometric and surface limits. This is not an overall ranking of service life, corrosion resistance or assembled-bearing performance.
Does an ABEC label identify the balls inside?
No. Keep assembled-bearing precision and loose-ball grade separate; neither should be inferred from the other without an explicit specification.
52100, carbon steel, 304, 316, 440C and acetal: compare the actual ball material
A steel-looking sphere is not a material specification. Identify the alloy and its condition before comparing corrosion, hardness or precision. These distinctions describe loose balls; the rings, cage and seals of a complete bearing need separate specifications.
For an existing assembly, preserve the specified ball diameter, material, grade, gauge and quantity together. Substituting a harder, more corrosion-resistant or lower-grade-number ball changes only some properties; it does not by itself validate the assembled bearing.
Ceramic is also an incomplete specification. Retain the named ceramic and its grade, not merely the colour. A loose ceramic ball, a hybrid bearing and an all-ceramic bearing are three different items.
On smaller screens, scroll the table sideways to read all columns.
| Material named in a search | What the manufacturer reference establishes | Selection limit |
|---|---|---|
| 52100 chrome steel | Abbott describes through-hardened bearing-alloy balls with high wear resistance, but no corrosion-resistance claim in its material table. | Chrome steel is not a promise of a chrome-plated or stainless surface. Keep lubrication and corrosion exposure in the assessment. |
| Carbon steel / mild steel | Abbott distinguishes soft, case-hardened and through-hardened carbon balls, and low- versus high-carbon compositions. | Do not transfer the performance of a through-hardened 52100 ball to an unidentified mild-steel ball. Coating and case depth are separate requirements. |
| 304 stainless | Abbott describes 304 balls for applications prioritizing corrosion resistance rather than hardness. | Record the exact alloy and condition. A stainless description alone does not establish rolling-contact load capacity. |
| 316 stainless | Abbott treats 316 as a separate stainless-ball material for corrosion-oriented applications, not as a synonym for 440C. | Identify the actual liquid, concentration and temperature. Do not interpret stainless as corrosion-proof or as an approval for food/medical use. |
| 440C stainless | Abbott's material table lists hardened 440C for bearing applications while describing its corrosion resistance as fair. | A 440C ball is not automatically a substitute for 304, 316 or chrome steel. Verify hardness, finish, size, grade and the assembly drawing. |
| Acetal / Delrin / Celcon | Abbott lists these plastic balls for low-load bearings, lightweight check valves and agitators, with its own plastic grade definitions. | Do not read a plastic Grade 1 as ISO steel-ball G3/G10 or an ABEC class. A material name is not a certified load or temperature limit. |
G10 vs G25 vs G100: read the standard before comparing the number
Selected values from Salem Specialty Ball's A.F.B.M.A. reference are shown below. Micrometre figures are calculated from its inch values using 25.4 mm per inch. This table is separate from the ISO table above; it is not a claim that the two standards are interchangeable.
In this reference G10 has tighter listed limits than G25, and G25 tighter than G100. None identifies nominal ball diameter, steel composition or assembled-bearing ABEC class. The supplier reference does not identify a standards edition: use the applicable specification and inspection certificate for acceptance, not this comparison alone.
On smaller screens, scroll the table sideways to read all columns.
| Ball grade | Published sphericity limit (in) | Calculated limit (µm) | Basic diameter tolerance (in) |
|---|---|---|---|
| G10 | 0.000010 | 0.254 | ±0.0001 |
| G25 | 0.000025 | 0.635 | ±0.0001 |
| G100 | 0.000100 | 2.54 | ±0.0005 |
| G1000 | 0.001000 | 25.4 | ±0.005 |
Metric ball diameter and nearby fractional sizes are different specifications
This calculated table covers nominal diameters in the keyword library. It is not an inventory or a table of balls inside specific bearings. Inch values are rounded to six decimals. For complete bearings, use bore d, outside D and width instead of this one-diameter table.
3/8 inch equals 9.525 mm, not 9.5 mm: the difference is 0.025 mm, or 25 µm. Likewise, 5/32 inch equals 3.96875 mm, not 4 mm; 1/4 inch equals 6.35 mm, not 6 mm. Rounding a shopping description is not a valid substitution rule.
A phrase such as '1 4 steel ball bearing' has lost the fraction slash and may also omit the unit. Confirm the original specification before treating it as 1/4 inch. A query such as '5×10×4 mm bearing' describes three boundary dimensions and belongs in complete-bearing search, not a loose-ball chart.
On smaller screens, scroll the table sideways to read all columns.
| Loose-ball nominal diameter (mm) | Calculated diameter (in) |
|---|---|
| 2 | 0.078740 |
| 3 | 0.118110 |
| 3.5 | 0.137795 |
| 4 | 0.157480 |
| 5 | 0.196850 |
| 6 | 0.236220 |
| 7 | 0.275591 |
| 8 | 0.314961 |
| 9 | 0.354331 |
| 9.5 | 0.374016 |
| 10 | 0.393701 |
| 11 | 0.433071 |
| 12 | 0.472441 |
| 13.5 | 0.531496 |
| 40 | 1.574803 |
How are steel bearing balls made?
A typical wire-based steel-ball process forms the sphere first, then controls hardness, geometry and surface finish. The sequence below is summarized from Abbott's manufacturing explanation; it is not a production recipe for every alloy or ceramic.
This describes ball manufacture, not the additional operations needed to make rings, cages or a complete bearing.
On smaller screens, scroll the table sideways to read all columns.
| Stage | Purpose |
|---|---|
| Form the blank | Cut wire and press it between dies to produce a near-spherical shape. |
| Remove the seam and soft-grind | Remove the raised die line and refine the shape before final finishing. |
| Apply material-specific heat treatment | Develop the required hardness; Abbott's carbon-steel example includes carburizing and hardening. |
| Remove scale and hard-grind | Remove heat-treatment residue, then control ball size and spherical form. |
| Lap and finish | Use finer finishing processes to reduce geometric and surface irregularities. |
| Inspect and retain lot identity | Verify the required properties. A polished appearance alone does not certify diameter variation, sphericity or grade. |
Estimate the mass of one solid ball without confusing it with a bearing assembly
For a homogeneous solid sphere, volume V = πd³/6. If diameter d is in mm and material density ρ is in g/cm³, mass in grams is m = πd³ρ/6000. This is a geometric estimate; use the actual material density, temperature and diameter for the part being assessed.
For illustration only, a 10 mm sphere at an assumed density of 7.85 g/cm³ weighs approximately 4.110 g. At the same assumed density a 1 inch (25.4 mm) sphere weighs approximately 67.355 g. These assumptions are not product specifications or measured catalogue masses.
The formula does not calculate the weight of a complete ball bearing, a hollow sphere or a coated composite ball. For a complete bearing use its recorded product mass; for a non-homogeneous ball each material volume must be accounted for.
What the evidence can — and cannot — tell you
| Observation or context | Interpretation to consider | Verification needed |
|---|---|---|
| Loose sphere | Use ball diameter | No bore, outside-ring diameter or cartridge width applies |
| Complete bearing marked 608 | Use a complete-bearing record | Its boundary dimensions do not specify its internal ball diameter or count |
| G10 or G100 | A ball-quality specification | Retain the standard and the required gauge or lot information |
| Steel or ceramic | A broad material description | Record the actual grade and suitability, not just colour or magnetism |
A practical investigation sequence
Identify and record
Identify whether the part is a loose ball, a caged ball set or a complete bearing. Keep the equipment and component position with the sample.
Check the context
Measure the ball with suitable calibrated equipment and record the units. A worn ball or a coarse calliper reading is not proof of its original grade or gauge.
Verify before acting
Obtain the specified material, nominal diameter, grade, gauge and quantity from the component drawing or service instruction. Do not substitute a nearby diameter because it is easier to find.
Keep the decision traceable
Keep the lot identification and inspection record. For an assembled bearing or a safety-critical hub, replacing individual balls is not automatically an approved repair method.
Capture the information a model search cannot guess
Keep this checklist with your inspection or comparison. Checking a box only records that you have collected the item; it does not certify the bearing.
0 of 4 information groups recorded.
Technical basis & editorial scope
Original BearingScope workflow, written for catalogue research and comparison. Manufacturer material is used to check principles, not copied as a product endorsement or substituted for model-specific instructions. Reviewed 1 October 2026.
- Redhill Precision — ISO 3290 precision-grade reference table — Selected G3, G5, G10, G20 and G100 geometric and surface values in µm; not the full normative standard
- Abbott Ball — Precision Balls — Loose-ball specification, precision and material distinctions
- Shimano — DM-LAHB004-01, HB-NN300 / FH-NN300 dealer manual — Named hub models only; grease specification, cleaning restrictions and model-specific ball sizes
- Salem Specialty Ball — ball grade reference — Selected A.F.B.M.A. ball-grade limits; standard and edition must be confirmed for acceptance. Inch-to-micrometre figures are explicit calculations.
- Abbott Ball — chrome steel balls — 52100 through-hardening and lack of corrosion-resistance claim; no stock or interchange claims.
- Abbott Ball — carbon steel balls — Carbon composition categories, soft, case-hardened and through-hardened options.
- Abbott Ball — 304 stainless balls — Corrosion-oriented material selection, not a guarantee of rolling-contact hardness or regulatory approval.
- Abbott Ball — 316 stainless balls — Distinct 316 material specification; no blanket corrosion or regulatory approval.
- Abbott Ball — 440C stainless balls — Hardened 440C bearing applications with bounded corrosion performance.
- Abbott Ball — plastic balls — Acetal applications and supplier-specific plastic-ball grade terminology, not steel-ball or ABEC equivalence.
- Abbott Ball — manufacturing process — Original concise explanation of a wire-based steel-ball forming and finishing sequence.
Source addresses and collection status are retained in the internal audit. No unpublished dimensions, torque settings, service intervals or interchange approvals are inferred.