51120 bearing: complete specifications & equivalents
The 51120 is a ISO 104 radial bearing sized 100 x 135 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 | 100 mm |
| Outer diameter D | 135 mm |
| Width B | 25 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 85 kN |
| Basic static load rating C0 | 268 kN |
| Fatigue load limit Pu | 11.2 kN |
| Limiting speed (mechanical) | 1700 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 987 g |
| Manufacturer designation | NTN 51120 |
| 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 & 51100-series range
| Bore d | 3.937 in |
|---|---|
| Outer diameter D | 5.315 in |
| Width B | 0.984 in |
| ISO bore code | 20 |
| Radial section height (D−d)/2 | 17.5 mm |
| Smallest bore in 51100-series | 10 mm |
| Largest outer diameter in 51100-series | 640 mm |
| Width range across 51100-series | 9–85 mm |
| Bore position in 51100-series (smallest first) | 20 of 46 |
| Bore above smallest 51100-series size | 90 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51120-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 51120 model number is decoded
NTN 51120 belongs to the light-section 51100 thrust family of single-direction thrust ball bearings: 100 / 135 / 25 mm (shaft bore / OD / height). NTN builds the number from 511 is the dimension series (light-section 51100 thrust family); 20 encodes the 100 mm bore (bore code x 5). Catalogue axial dynamic rating Ca is 85 kN against C0a 268 kN — a static/dynamic ratio of 3.15 that is the signature of a thrust raceway. Choose the light-section 51100 thrust family when the shaft carries pure thrust in one direction at moderate speed — vertical shafts are the textbook case. The housing washer needs radial freedom in its seat so the bearing can centre itself; clamping it radially defeats the self-centring the loose fit is designed to give.
Typical equipment & failure modes
Common applications
- large rotary-table and index-table thrust rings
- vertical water-pump and turbine thrust blocks
- large crane hook and swivel assemblies
- rolling-mill screwdown and adjustment screws
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
- rapid flaking after radial load was allowed onto the bearing — a single-direction thrust ball bearing carries axial load only
- contamination pitting from particles settling on the horizontal housing washer — the classic failure of vertical-shaft grease-lubricated seats
- lubricant starvation scoring on the raceway track when grease is thrown outward by centrifugal effect and never replaced
Selection pitfalls — read before you substitute
- At 100 mm bore the washers are heavy enough to sag out of square during assembly — support the stack horizontally where possible and verify face runout before loading.
- The 511 light section is the speed-friendly end of the thrust-ball plan — for the same 100 mm bore it gives up load to gain OD, height and limiting-speed headroom.
- Radial load is the silent killer here: a belt pull or gear force on the same shaft must land on a radial bearing, because 51120 has no radial capacity at all.
- Single-direction means exactly that: thrust on 51120 in the wrong direction separates the washers and drops the ball set — if reversal is possible even during coast-down, engineer against it.
- Swapping the shaft and housing washers is an easy assembly error on the 100 mm size — the bores differ only slightly, but the wrong pairing walks off-centre under load.
- The Ca 85/C0a 268 kN ratings and 11.2 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51120; 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 51120?
51120 is a single-direction thrust ball bearing to ISO 104: 100 mm shaft-washer bore, 135 mm outside diameter, 25 mm stack height (3.937 x 5.315 x 0.984 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 85 kN, C0a 268 kN and a 11.2 kN fatigue load limit Pu; the grease limiting speed is 1,700 r/min and the oil rating 2,400 r/min; mass about 987 g.
How is the 51120 designation structured?
511 is the dimension series (light-section 51100 thrust family); 20 encodes the 100 mm bore (bore code x 5). The 135 mm OD and 25 mm height follow the ISO 104 boundary plan for that series.
Can 51120 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 51120?
At the 1,700 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 51120?
The 100/135/25 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 85 kN / C0a 268 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.