51211 bearing: complete specifications & equivalents
The 51211 is a ISO 104 radial bearing sized 55 x 90 x 25 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 55 mm |
| Outer diameter D | 90 mm |
| Width B | 25 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 69.5 kN |
| Basic static load rating C0 | 159 kN |
| Fatigue load limit Pu | 7.15 kN |
| Limiting speed (mechanical) | 2100 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 608 g |
| Manufacturer designation | NTN 51211 |
| 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 | 2.165 in |
|---|---|
| Outer diameter D | 3.543 in |
| Width B | 0.984 in |
| ISO bore code | 11 |
| Radial section height (D−d)/2 | 17.5 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) | 12 of 39 |
| Bore above smallest 51200-series size | 45 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51211-SKF | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 55×90×25 mm envelope per ISO 15; catalogue load ratings differ by >10% — re-rate the application before substituting. |
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 51211 model number is decoded
NTN 51211 belongs to the medium-section 51200 thrust family of single-direction thrust ball bearings: 55 / 90 / 25 mm (shaft bore / OD / height). Two fields make up the code — 512 is the dimension series (medium-section 51200 thrust family) and 11 encodes the 55 mm bore (bore code x 5). The ball-and-cage set is separable from both washers, which is why the mounting order (shaft washer first, then cage, then housing washer) matters. Choose the medium-section 51200 thrust family when the shaft carries pure thrust in one direction at moderate speed — vertical shafts are the textbook case. The shaft washer (bore 55 mm, tight on the shaft) and the housing washer (slightly looser bore) are not interchangeable — check the catalogue bore codes before pressing anything on.
Typical equipment & failure modes
Common applications
- press and punch-machine thrust seats
- conveyor vertical-drive thrust positions
- vertical motor and pump thrust shoes
- machine-tool tailstock and steady-rest screws
Known failure patterns
- cage pocket wear and ball skid polish after long running below the minimum axial load, the balls sliding instead of rolling on the washers
- housing-washer rocking on an out-of-square support face, seen as uneven wear around the raceway circle and rising running torque
- rapid flaking after radial load was allowed onto the bearing — a single-direction thrust ball bearing carries axial load only
- lubricant starvation scoring on the raceway track when grease is thrown outward by centrifugal effect and never replaced
- cage breakage after repeated shock reversal banged the ball set against the pocket bridges
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 55 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 55 mm bore.
- The C0a of 159 kN is a static rating: sizing continuous working thrust from C0a alone overstates what the raceway survives.
- Grease in a horizontal-washer seat stays only if the housing is designed to hold it; open vertical arrangements need an oil bath or a grease-retaining cover.
- Radial load is the silent killer here: a belt pull or gear force on the same shaft must land on a radial bearing, because 51211 has no radial capacity at all.
- The Ca 69.5/C0a 159 kN ratings and 7.15 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51211; 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 51211?
51211 is a single-direction thrust ball bearing to ISO 104: 55 mm shaft-washer bore, 90 mm outside diameter, 25 mm stack height (2.165 x 3.543 x 0.984 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 69.5 kN, C0a 159 kN and a 7.15 kN fatigue load limit Pu; the grease limiting speed is 2,100 r/min and the oil rating 3,000 r/min; mass about 608 g.
How is the 51211 designation structured?
512 is the dimension series (medium-section 51200 thrust family); 11 encodes the 55 mm bore (bore code x 5). The 90 mm OD and 25 mm height follow the ISO 104 boundary plan for that series.
Can 51211 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 51211?
At the 2,100 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 51211?
The 55/90/25 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 69.5 kN / C0a 159 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.