51210 bearing: complete specifications & equivalents
The 51210 is a ISO 104 radial bearing sized 50 x 78 x 22 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 50 mm |
| Outer diameter D | 78 mm |
| Width B | 22 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 48.5 kN |
| Basic static load rating C0 | 111 kN |
| Fatigue load limit Pu | 5.05 kN |
| Limiting speed (mechanical) | 2400 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 378 g |
| Manufacturer designation | NTN 51210 |
| Standard | ISO 104 |
| Catalog version | NTN Ball and Roller Bearings CAT.No.2203E |
| Last verified | 2026-10-01 |
Source: catalog reference (NTN Ball and Roller Bearings CAT.No.2203E) · extracted 2026-10-01
Parameters extracted from the official NTN Ball and Roller Bearings catalogue (NTN Ball and Roller Bearings CAT.No.2203E); NTN® is a trademark of NTN Corporation, used here for identification only — mpnbase is not an authorized NTN distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at ntnglobal.com.
Dimensions in inches & 51200-series range
| Bore d | 1.969 in |
|---|---|
| Outer diameter D | 3.071 in |
| Width B | 0.866 in |
| ISO bore code | 10 |
| Radial section height (D−d)/2 | 14 mm |
| Smallest bore in 51200-series | 10 mm |
| Largest outer diameter in 51200-series | 520 mm |
| Width range across 51200-series | 11–112 mm |
| Bore position in 51200-series (smallest first) | 11 of 39 |
| Bore above smallest 51200-series size | 40 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51210-SKF | SKF | full Dimensions and internal design equivalent — standard interchange. | Identical ISO 15 envelope, seal and ratings band — standard interchange; re-verify precision class and clearance per supplier. |
Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.
How the 51210 model number is decoded
In NTN Ball and Roller Bearings CAT.No.2203E, 51210 appears as a medium-section 51200 thrust family bearing with a 50 mm shaft washer, a 78 mm housing diameter and 22 mm of stack height. Reading the code: 512 is the dimension series (medium-section 51200 thrust family), and 10 encodes the 50 mm bore (bore code x 5). The washer section here is 14.0 mm of radial height, and the catalogue couples it with Ca 48.5 kN / C0a 111 kN. Selection starts from the load direction: if thrust ever reverses, plan a second thrust bearing (or a double-direction execution) rather than relying on the unloaded raceway. On a vertical shaft, pack grease between the washers and plan a relubrication path — centrifugal effect drives grease outward and the track runs dry without it.
Typical equipment & failure modes
Common applications
- extruder and mixer thrust housings
- winch and capstan vertical shafts
- press and punch-machine thrust seats
- conveyor vertical-drive thrust positions
Known failure patterns
- ball and raceway smearing from gyroscopic spin when the bearing runs fast under too little axial load — the minimum-load rule exists exactly for this
- fretting between shaft washer and shaft when the seat is cut loose — the washer creeps, the centre line shifts and the balls start running off-track
- early fatigue from thrust reversal hammering the unloaded raceway, because the bearing has no contact surfaces for the opposite direction
- edge loading from a shaft washer mounted off-centre, cutting the contact ellipse short at one side of the track
- edge loading from a shaft washer mounted off-centre, cutting the contact ellipse short at one side of the track
Selection pitfalls — read before you substitute
- In this size class the frequent miss is washer identification: keep the catalogued shaft/housing washer pairing of the 50 mm size together from unpacking to assembly.
- The 512 medium section is the default choice: balanced height and capacity for general vertical-shaft duty at 50 mm bore.
- Swapping the shaft and housing washers is an easy assembly error on the 50 mm size — the bores differ only slightly, but the wrong pairing walks off-centre under load.
- Swapping the shaft and housing washers is an easy assembly error on the 50 mm size — the bores differ only slightly, but the wrong pairing walks off-centre under load.
- The C0a of 111 kN is a static rating: sizing continuous working thrust from C0a alone overstates what the raceway survives.
- The Ca 48.5/C0a 111 kN ratings and 5.05 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51210; raceway geometry legitimately differs between manufacturers, so re-verify ratings and washer identification before substituting another make.
Frequently asked questions
What are the dimensions and catalogue ratings of NTN 51210?
51210 is a single-direction thrust ball bearing to ISO 104: 50 mm shaft-washer bore, 78 mm outside diameter, 22 mm stack height (1.969 x 3.071 x 0.866 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 48.5 kN, C0a 111 kN and a 5.05 kN fatigue load limit Pu; the grease limiting speed is 2,400 r/min and the oil rating 3,400 r/min; mass about 378 g.
How is the 51210 designation structured?
512 is the dimension series (medium-section 51200 thrust family); 10 encodes the 50 mm bore (bore code x 5). The 78 mm OD and 22 mm height follow the ISO 104 boundary plan for that series.
Can 51210 carry radial load or reversing thrust?
No. The raceways contact the balls at 90 deg to the shaft, so the rating is purely axial and single-direction. Radial load must be carried by a separate radial bearing, and reversing thrust needs a second thrust bearing or a double-direction execution.
Why does NTN specify a minimum axial load for 51210?
At the 2,400 r/min class speed, centrifugal and gyroscopic effects make an under-loaded ball set skid and smear instead of roll. The catalogue minimum-load formula gives the axial preload — from the machine weight, springs or a dead-weight — that keeps the contact rolling.
What should be checked before substituting another make for 51210?
The 50/78/22 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 48.5 kN / C0a 111 kN, the speed figures and the shaft/housing washer identification against the donor catalogue.
Reviewed & verified by the MPN Base engineering desk against source catalog NTN Ball and Roller Bearings CAT.No.2203E on 2026-10-01. Read our editorial & correction policy.