Jewel Bearings: Ruby, Sapphire, Ring, Vee, Cup & Watch Pivots
A jewel bearing uses a hard, polished jewel surface to support a small pivot or shaft. Synthetic ruby and sapphire are common materials. Ring, vee, cup and endstone designs provide different contact geometries; they are not miniature ball bearings and cannot be selected from outside diameter alone.
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Ring vs vee vs cup vs endstone
Select the contact geometry and load direction before comparing material or size.
Swiss Jewel describes these as distinct design arrangements. A ring may guide a shaft without supplying the required end-thrust support. A catalogue drawing of one loose jewel does not describe the entire pivot assembly.
On smaller screens, scroll the table sideways to read all columns.
| Form | Typical support arrangement | Comparison priority |
|---|---|---|
| Ring | A cylindrical shaft runs through the jewel; an olive hole has a radiused profile | Hole geometry, shaft clearance and alignment |
| Vee | A radiused conical pivot seats in the jewel | Pivot/seat radius, included angle and depth |
| Cup | A rounded pivot works against a cup-shaped seat | Pivot shape, orientation and restraint |
| Endstone | An end-contact surface takes thrust, often alongside a ring jewel | End-play and the matching pivot/ring arrangement |
Where jewel bearings are used
Swiss Jewel documents precision-instrument and timekeeping uses. These are application examples, not approval for a named device.
For a concrete watch example, Seiko lists 24 jewels for calibre 6R55 and describes its Diashock arrangement at shock-sensitive locations such as the balance-wheel pivot. The number 24 is not a jewel size, a bearing grade or a set of 24 interchangeable parts.
On smaller screens, scroll the table sideways to read all columns.
| Application | Why geometry matters | Identity still required |
|---|---|---|
| Indicating meters and instruments | A light moving element may use a vee/pivot support | Moving assembly, pivot and mount drawing |
| Compasses and flow-measurement devices | Cup and ring arrangements serve different shaft layouts | Orientation, fluid exposure and instrument design |
| Watch and clock movements | Pivot guidance and end-thrust arrangements are component-specific | Calibre, wheel/pivot position and service part identity |
Two source-labelled sapphire Vee examples
Bird Precision's stock table labels the radius, depth and outside-diameter fields at an 80-degree angle. The original inch values are shown without extending them to another angle or converting them into a fit recommendation.
These examples differ in more than outside diameter. The stock summary does not supply a complete pivot, assembly load limit or device compatibility. Preserve the angle qualification and obtain the selected part's controlled drawing before specifying a mating pivot. Blank fields in other catalogue entries are not treated as zero.
On smaller screens, scroll the table sideways to read all columns.
| Item | Seat radius at 80° | Seat depth at 80° | Outside diameter at 80° |
|---|---|---|---|
| RB21002 | 0.003 in | 0.01 in | 0.0394 in |
| RB21125 | 0.0012 in | 0.0142 in | 0.0469 in |
A useful jewel-bearing comparison record
On smaller screens, scroll the table sideways to read all columns.
| Record | Do not replace it with |
|---|---|
| Jewel shape and material | Colour or a generic ruby/sapphire label |
| Shaft or pivot contact geometry | Only the outside diameter of the jewel |
| Drawing tolerances and units | Rounded dimensions from a photograph |
| Housing, retention and end-play | A universal press-fit or tightening instruction |
| Service lubrication and shock arrangement | A claim that all jewels run dry or survive all shocks |
Is a jewel bearing the same as a ceramic ball bearing?
No. The forms described here use a polished contact seat or bore for a pivot. A ball bearing uses rolling elements and raceways; sharing a hard material does not make the assemblies equivalent.
Does a higher watch jewel count prove better accuracy?
Jewel count alone is not an accuracy specification. Compare the complete movement's published performance and construction instead.
Can I install one of these stock jewels in a particular watch or turntable?
Only an exact drawing and assembly match could establish that. No device-specific interchange is inferred from these two stock examples.
What the evidence can — and cannot — tell you
| Observation or context | Interpretation to consider | Verification needed |
|---|---|---|
| Ruby or sapphire description | A material identification, not a complete bearing specification | Confirm geometry, hole or tip dimensions, finish and mounting. |
| Ring jewel | Radial guidance for a shaft or pivot | Check straight versus radiused hole, clearance and separate thrust support. |
| Vee jewel | A seat used with an appropriately shaped pivot | Match included angle, seat radius/depth and pivot geometry. |
| Watch jewel count | A movement specification | Identify the calibre and component position before looking for a replacement. |
A practical investigation sequence
Identify and record
Record the instrument or watch calibre, pivot position and the complete jewel assembly. Photograph the mounting without assuming that colour identifies the grade.
Check the context
Separate radial guidance from end-thrust support. Record the jewel, pivot, mount and any spring or endstone as distinct components.
Verify before acting
Compare the original drawing's dimensions, tolerances and units with a documented part. A close outside diameter alone is not a match.
Keep the decision traceable
Keep lubrication, adjustment and mounting instructions with the exact assembly. Do not improvise a press fit or interpret a jewel's hardness as immunity to mounting damage.
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.
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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.
- Bird Precision — Stock sapphire Vee table; original inch fields — Principles and explicitly named examples only; not an equipment fitment or universal rating. Source reviewed 3 October 2026.
- Swiss Jewel — Jewel bearing geometry and applications — Principles and explicitly named examples only; not an equipment fitment or universal rating. Source reviewed 3 October 2026.
- Seiko — Calibre 6R55 jewel count and Diashock description — Principles and explicitly named examples only; not an equipment fitment or universal rating. Source reviewed 3 October 2026.
Source addresses and collection status are retained in the internal audit. No unpublished dimensions, torque settings, service intervals or interchange approvals are inferred.