51124-NTN bearing: complete specifications & equivalents
The 51124-NTN is a ISO 104 radial bearing sized 120 x 155 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 | 120 mm |
| Outer diameter D | 155 mm |
| Width B | 25 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 89 kN |
| Basic static load rating C0 | 310 kN |
| Fatigue load limit Pu | 11.8 kN |
| Limiting speed (mechanical) | 1500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1110 g |
| Manufacturer designation | NTN 51124 |
| 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 | 4.724 in |
|---|---|
| Outer diameter D | 6.102 in |
| Width B | 0.984 in |
| ISO bore code | 24 |
| 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) | 22 of 46 |
| Bore above smallest 51100-series size | 110 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the 51124-NTN model number is decoded
51124 is an NTN single-direction thrust ball bearing of the light-section 51100 thrust family: 120 mm bore, 155 mm outside diameter, 25 mm overall height in NTN Ball and Roller Bearings CAT.No.2203E. NTN builds the number from 511 is the dimension series (light-section 51100 thrust family); 24 encodes the 120 mm bore (bore code x 5). Catalogue mass is about 1110 g for the full washer-and-cage stack. 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. After assembly, rotate under light load and check torque and temperature rise — a thrust ball bearing mounted with the washers swapped runs, but fails fast.
Typical equipment & failure modes
Common applications
- large marine winch and windlass shafts
- heavy press and mill screwdown thrust seats
- crane slew-ring auxiliary thrust positions
- large mixer and reactor vertical shafts
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
- edge loading from a shaft washer mounted off-centre, cutting the contact ellipse short at one side of the track
- lubricant starvation scoring on the raceway track when grease is thrown outward by centrifugal effect and never replaced
Selection pitfalls — read before you substitute
- For a 120 mm bore thrust bearing, the seating surfaces and oil supply decide service life; at this size a field-improvised housing is the usual root cause behind "premature" failures.
- The 511 light section is the speed-friendly end of the thrust-ball plan — for the same 120 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 51124 has no radial capacity at all.
- Single-direction means exactly that: thrust on 51124 in the wrong direction separates the washers and drops the ball set — if reversal is possible even during coast-down, engineer against it.
- The 1,500 r/min speed figure assumes the catalogue lubrication state; at high speed the limiting factor is often the minimum load, not the rating table.
- The Ca 89/C0a 310 kN ratings and 11.8 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51124; 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 51124?
51124 is a single-direction thrust ball bearing to ISO 104: 120 mm shaft-washer bore, 155 mm outside diameter, 25 mm stack height (4.724 x 6.102 x 0.984 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 89 kN, C0a 310 kN and a 11.8 kN fatigue load limit Pu; the grease limiting speed is 1,500 r/min and the oil rating 2,200 r/min; mass about 1110 g.
How is the 51124 designation structured?
511 is the dimension series (light-section 51100 thrust family); 24 encodes the 120 mm bore (bore code x 5). The 155 mm OD and 25 mm height follow the ISO 104 boundary plan for that series.
Can 51124 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 51124?
At the 1,500 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 51124?
The 120/155/25 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 89 kN / C0a 310 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.