61918 Single-row Deep Groove Ball Bearing
61918 is a single-row deep groove ball bearing, thin series, with a 90 mm bore, a 125 mm outside diameter and a 18 mm width. Those numbers — the bore, outside diameter, width and the 1.1 mm minimum chamfer — are ISO 15 standard values, identical for every manufacturer.
Dimensions
All 61900 Series designations- Designation
- 61918
- Type
- Single-row deep groove ball bearing — radial
- Series
- 61900 Series (thin)
- Bore code
- 18 — 90 mm
- Bore d
- 90 mm (3.5433 in)
- outside diameter D
- 125 mm
- width B
- 18 mm — the assembled width
- Chamfer, r s min
- 1.1 mm — minimum, not nominal
- Radial section
- 17.5 mm = (D − d) / 2
Nominal values in millimetres as published in ISO 15, the boundary dimension plan this type is tabulated in. The chamfer figure is the minimum single chamfer dimension the plan gives (r s min); the matching maximum is in ISO 582 — which is why the row says “min” and not an equality. 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 90 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 18 gives 90 mm. The four exceptions are 00, 01, 02 and 03 at 10, 12, 15 and 17 mm. This one is also sold as 6918 — the same series under the other naming convention, where 61800 is the SKF / FAG form and 6800 the NSK form. Both designations take the same 90 mm shaft and the same housing.
Position in the series19 of 21 in 61900 Series
Radial internal clearanceISO 5753-1, bore 80–100 mm
| Group | Radial internal clearance | When it is used |
|---|---|---|
| C2 | 1–18 µm | Tighter than default; for fits that already take up the clearance. |
| CN (normal) | 12–36 µm | The default — usually not marked on the bearing at all. |
| C3 | 30–58 µm | Interference fits, electric motors, hot inner ring. The common upgrade. |
| C4 | 53–84 µm | Heavy interference fits and high-temperature service. |
| C5 | 75–120 µm | The loosest group in the table; special applications. |
Values are the pre-mounting radial internal clearance for a single-row deep groove ball bearing with a cylindrical bore, in micrometres, from ISO 5753-1. Pressing the inner ring onto a shaft and running the inner ring hotter than the outer ring both close this up — an interference of a few micrometres is a few micrometres straight out of the running clearance, which is the whole reason C3 exists. For this bore, normal (CN) is 12–36 µm and C3 is 30–58 µm.
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, ISO 1206, ISO 3245) 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 90 mm shaft would take instead
| Designation | Series | Type | D | Overall size (B / T / H) | Section (D − d)/2 | vs 61918 |
|---|---|---|---|---|---|---|
| 61918 | Thin — this bearing | Deep groove ball | 125 | 18 B | 17.5 | — |
| 61718 | 61700 Series — Extra-thin | Deep groove ball | 110 | 10 B | 10 | -15 mm on D, -8 mm B |
| 61818 | 61800 Series — Ultra-thin | Deep groove ball | 115 | 13 B | 12.5 | -10 mm on D, -5 mm B |
| 51118 | 51100 Series — Light | Thrust ball | 120 | 22 H | 15 | -5 mm on D, +4 mm H |
| NA4918 | NA 49 Series — Light | Needle roller | 125 | 35 B | 17.5 | 0 mm on D, +17 mm B |
| NA5918 | NA 59 Series — Light, wide | Needle roller | 125 | 46 B | 17.5 | 0 mm on D, +28 mm B |
| NA6918 | NA 69 Series — Light, extra wide | Needle roller | 125 | 63 B | 17.5 | 0 mm on D, +45 mm B |
| 51218 | 51200 Series — Medium | Thrust ball | 135 | 35 H | 22.5 | +10 mm on D, +17 mm H |
| 6018 | 6000 Series — Extra-light | Deep groove ball | 140 | 24 B | 25 | +15 mm on D, +6 mm B |
| 16018 | 16000 Series — Narrow | Deep groove ball | 140 | 16 B | 25 | +15 mm on D, -2 mm B |
| 6218 | 6200 Series — Light | Deep groove ball | 160 | 30 B | 35 | +35 mm on D, +12 mm B |
| 1218 | 1200 Series — Light | Self-aligning ball | 160 | 30 B | 35 | +35 mm on D, +12 mm B |
| 2218 | 2200 Series — Light, wide | Self-aligning ball | 160 | 40 B | 35 | +35 mm on D, +22 mm B |
| 30218 | 30200 Series — Light | Tapered roller | 160 | 32.5 T | 35 | +35 mm on D, +14.5 mm T |
| NU218 | NU 2 Series — Light | Cylindrical roller | 160 | 30 B | 35 | +35 mm on D, +12 mm B |
| NU2218 | NU 22 Series — Wide light | Cylindrical roller | 160 | 40 B | 35 | +35 mm on D, +22 mm B |
| 22218 | 222 Series — Wide light | Spherical roller | 160 | 40 B | 35 | +35 mm on D, +22 mm B |
| 6318 | 6300 Series — Medium | Deep groove ball | 190 | 43 B | 50 | +65 mm on D, +25 mm B |
| 1318 | 1300 Series — Medium | Self-aligning ball | 190 | 43 B | 50 | +65 mm on D, +25 mm B |
| 2318 | 2300 Series — Medium, wide | Self-aligning ball | 190 | 64 B | 50 | +65 mm on D, +46 mm B |
| 30318 | 30300 Series — Medium | Tapered roller | 190 | 46.5 T | 50 | +65 mm on D, +28.5 mm T |
| 21318 | 213 Series — Medium | Spherical roller | 190 | 43 B | 50 | +65 mm on D, +25 mm B |
| 22318 | 223 Series — Wide medium | Spherical roller | 190 | 64 B | 50 | +65 mm on D, +46 mm B |
| 6418 | 6400 Series — Heavy | Deep groove ball | 225 | 54 B | 67.5 | +100 mm on D, +36 mm B |
24 series across seven 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 15 / ISO 355 / ISO 104 / ISO 15 / ISO 15 / ISO 1206 / ISO 1206 / ISO 3245) — the same figure for every manufacturer. The section column is derived as (D − d) / 2. Where two rows share the outside diameter the last column carries the width as well, because that is then the whole of the difference: the 49, 59 and 69 needle series share one envelope at every bore they have in common and differ only in standing 13, 18 and 23 mm wide. 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.