51256 bearing: complete specifications & equivalents
The 51256 is a ISO 104 radial bearing sized 280 x 380 x 80 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 280 mm |
| Outer diameter D | 380 mm |
| Width B | 80 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 460 kN |
| Basic static load rating C0 | 1970 kN |
| Fatigue load limit Pu | 49 kN |
| Limiting speed (mechanical) | 510 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 26100 g |
| Manufacturer designation | NTN 51256 |
| 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 | 11.024 in |
|---|---|
| Outer diameter D | 14.961 in |
| Width B | 3.15 in |
| ISO bore code | 56 |
| Radial section height (D−d)/2 | 50 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) | 34 of 39 |
| Bore above smallest 51200-series size | 270 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the 51256 model number is decoded
51256 is the 280 mm member of NTN's medium-section 51200 thrust family: 380 mm across the washers, 80 mm tall. The designation is 512 is the dimension series (medium-section 51200 thrust family) plus 56 encodes the 280 mm bore (bore code x 5). With Ca 460 kN and C0a 1970 kN, each mm of shaft bore carries about 1.64 kN of dynamic axial rating. For a 280 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
- bulk-handler stacker/reclaimer thrust pivots
- heavy rotary furnace and kiln thrust points
- vertical hydro and pump-turbine thrust supports
- large marine winch and windlass 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
- 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
- cage breakage after repeated shock reversal banged the ball set against the pocket bridges
- 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 280 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 280 mm bore.
- Swapping the shaft and housing washers is an easy assembly error on the 280 mm size — the bores differ only slightly, but the wrong pairing walks off-centre under load.
- The C0a of 1970 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.
- The Ca 460/C0a 1970 kN ratings and 49 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51256; 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 51256?
51256 is a single-direction thrust ball bearing to ISO 104: 280 mm shaft-washer bore, 380 mm outside diameter, 80 mm stack height (11.024 x 14.961 x 3.15 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 460 kN, C0a 1970 kN and a 49 kN fatigue load limit Pu; the grease limiting speed is 510 r/min and the oil rating 730 r/min; mass about 26100 g.
How is the 51256 designation structured?
512 is the dimension series (medium-section 51200 thrust family); 56 encodes the 280 mm bore (bore code x 5). The 380 mm OD and 80 mm height follow the ISO 104 boundary plan for that series.
Can 51256 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 51256?
At the 510 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 51256?
The 280/380/80 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 460 kN / C0a 1970 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.