51208 Single-row Single-direction Thrust Ball Bearing
51208 is a single-row single-direction thrust ball bearing, medium series, with a 40 mm bore, a 68 mm outside diameter and a 19 mm overall height. Those three numbers are ISO 104 standard values, identical for every manufacturer.
Dimensions
All 51200 Series designations- Designation
- 51208
- Type
- Single-row single-direction thrust ball bearing — axial
- Series
- 51200 Series (medium)
- Bore code
- 08 — 40 mm
- Bore d
- 40 mm (1.5748 in)
- outside diameter D
- 68 mm
- overall height H
- 19 mm — the assembled height
- Radial section
- 14 mm = (D − d) / 2
Nominal values in millimetres as published in ISO 104, the boundary dimension plan this type is tabulated in. This type is not tabulated with a chamfer here: ISO 104 gives a tapered roller two separate values while the catalogues consulted publish only one of them, and the thrust tables contradict each other inside a single table — so no chamfer figure meets this library’s rule of a checkable second source, and none is printed. That is an absence, not a zero. A bearing that has been fitted with shields or seals carries the same dimensions, because none of the suffixes touches the boundary dimension plan.
Reading the designationwhere 40 mm comes from
The designation is three fields: type, the series and the bore code. For codes 04 and above the bore is the code multiplied by five, which is why 08 gives 40 mm. The four exceptions are 00, 01, 02 and 03 at 10, 12, 15 and 17 mm.
Position in the series9 of 20 in 51200 Series
No radial clearance table on this pagesingle-row single-direction thrust ball bearing
A thrust ball bearing has no radial clearance to state. It carries axial load in one direction only, and the internal “clearance” that matters is the axial gap inside the ball and cage set, which the boundary dimension plan does not fix. The bore of a 51-series bearing also falls inside the span the clearance table covers, so a radial clearance row can be looked up for it — but it would be a row about a different kind of bearing, and printing it here would be a correct number under a wrong heading.
What is deliberately not publishedwhy there is no load rating here
No load rating, no limiting speed and no mass appears on this page. Those are catalogue values rather than standard values: ISO 281 defines how a dynamic rating is calculated, not what it comes out as, and the result depends on internal geometry — ball or roller diameter, the complement, raceway conformity — that none of the boundary dimension plans (ISO 15, ISO 355, ISO 104) fixes. Published catalogue figures for one and the same designation differ between makes by several percent at these sizes, and limiting speed additionally depends on lubrication and on whether the bearing is open, shielded or sealed. Publishing any single figure here would dress a catalogue entry up as a property of the designation. Take the rating from the catalogue of the bearing you actually buy.
The dimensions above are a different matter, and they are the reason a designation is worth anything: the boundary dimensions — bore, outside diameter and the section dimensions of the plan this type is tabulated in, plus the chamfer minimum where that plan gives one — are fixed by the standard, so every maker's bearing of this designation fits the same shaft and the same housing.
Same bore, every series and typewhat a 40 mm shaft would take instead
| Designation | Series | Type | D | Overall size (B / T / H) | Section (D − d)/2 | vs 51208 |
|---|---|---|---|---|---|---|
| 51208 | Medium — this bearing | Thrust ball | 68 | 19 H | 14 | — |
| 61708 | 61700 Series — Extra-thin | Deep groove ball | 50 | 6 B | 5 | -18 mm on D |
| 61808 | 61800 Series — Ultra-thin | Deep groove ball | 52 | 7 B | 6 | -16 mm on D |
| 51108 | 51100 Series — Light | Thrust ball | 60 | 13 H | 10 | -8 mm on D |
| 61908 | 61900 Series — Thin | Deep groove ball | 62 | 12 B | 11 | -6 mm on D |
| 6008 | 6000 Series — Extra-light | Deep groove ball | 68 | 15 B | 14 | 0 mm on D |
| 16008 | 16000 Series — Narrow | Deep groove ball | 68 | 9 B | 14 | 0 mm on D |
| 6208 | 6200 Series — Light | Deep groove ball | 80 | 18 B | 20 | +12 mm on D |
| 30208 | 30200 Series — Light | Tapered roller | 80 | 19.75 T | 20 | +12 mm on D |
| 6308 | 6300 Series — Medium | Deep groove ball | 90 | 23 B | 25 | +22 mm on D |
| 30308 | 30300 Series — Medium | Tapered roller | 90 | 25.25 T | 25 | +22 mm on D |
| 6408 | 6400 Series — Heavy | Deep groove ball | 110 | 27 B | 35 | +42 mm on D |
12 series across three bearing types, one bore: the shaft diameter is the same in every row, so the only thing that changes is what the housing and the axial space have to accommodate. Outside diameter and the overall size are standard boundary dimensions in the plan each type is tabulated in (ISO 15 / ISO 355 / ISO 104) — the same figure for every manufacturer. The section column is derived as (D − d) / 2. Load capacity rises with the outside diameter, but the figure itself has to come from the manufacturer’s catalogue for the bearing you actually buy — see above.