51224-NTN bearing: complete specifications & equivalents
The 51224-NTN is a ISO 104 radial bearing sized 120 x 170 x 39 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 | 170 mm |
| Width B | 39 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 154 kN |
| Basic static load rating C0 | 470 kN |
| Fatigue load limit Pu | 17.7 kN |
| Limiting speed (mechanical) | 1200 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 2710 g |
| Manufacturer designation | NTN 51224 |
| 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 | 4.724 in |
|---|---|
| Outer diameter D | 6.693 in |
| Width B | 1.535 in |
| ISO bore code | 24 |
| Radial section height (D−d)/2 | 25 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) | 22 of 39 |
| Bore above smallest 51200-series size | 110 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the 51224-NTN model number is decoded
In NTN Ball and Roller Bearings CAT.No.2203E, 51224 appears as a medium-section 51200 thrust family bearing with a 120 mm shaft washer, a 170 mm housing diameter and 39 mm of stack height. The designation is 512 is the dimension series (medium-section 51200 thrust family) plus 24 encodes the 120 mm bore (bore code x 5). Because the contact points run at 90 deg to the shaft, none of the rating is available for radial load — not even incidentally. For a 120 mm shaft with combined radial-plus-axial load, pair this bearing with a separate radial bearing — the thrust ball bearing must never be asked to carry the radial share. 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 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
- 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
- housing-washer rocking on an out-of-square support face, seen as uneven wear around the raceway circle and rising running torque
- early fatigue from thrust reversal hammering the unloaded raceway, because the bearing has no contact surfaces for the opposite direction
- washer face corrosion under long standstill in humid service, later printed into the raceway as evenly spaced pitting
- contamination pitting from particles settling on the horizontal housing washer — the classic failure of vertical-shaft grease-lubricated seats
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 512 medium section is the default choice: balanced height and capacity for general vertical-shaft duty at 120 mm bore.
- Radial load is the silent killer here: a belt pull or gear force on the same shaft must land on a radial bearing, because 51224 has no radial capacity at all.
- Below the minimum axial load the balls skid; the catalogue Ca of 154 kN never saves a bearing that is running too lightly loaded at 1,200 r/min.
- Single-direction means exactly that: thrust on 51224 in the wrong direction separates the washers and drops the ball set — if reversal is possible even during coast-down, engineer against it.
- The Ca 154/C0a 470 kN ratings and 17.7 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51224; 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 51224?
51224 is a single-direction thrust ball bearing to ISO 104: 120 mm shaft-washer bore, 170 mm outside diameter, 39 mm stack height (4.724 x 6.693 x 1.535 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 154 kN, C0a 470 kN and a 17.7 kN fatigue load limit Pu; the grease limiting speed is 1,200 r/min and the oil rating 1,700 r/min; mass about 2710 g.
How is the 51224 designation structured?
512 is the dimension series (medium-section 51200 thrust family); 24 encodes the 120 mm bore (bore code x 5). The 170 mm OD and 39 mm height follow the ISO 104 boundary plan for that series.
Can 51224 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 51224?
At the 1,200 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 51224?
The 120/170/39 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 154 kN / C0a 470 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.