51234 bearing: complete specifications & equivalents
The 51234 is a ISO 104 radial bearing sized 170 x 240 x 55 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 170 mm |
| Outer diameter D | 240 mm |
| Width B | 55 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 261 kN |
| Basic static load rating C0 | 835 kN |
| Fatigue load limit Pu | 26.3 kN |
| Limiting speed (mechanical) | 810 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 7810 g |
| Manufacturer designation | NTN 51234 |
| 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 | 6.693 in |
|---|---|
| Outer diameter D | 9.449 in |
| Width B | 2.165 in |
| ISO bore code | 34 |
| Radial section height (D−d)/2 | 35 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) | 27 of 39 |
| Bore above smallest 51200-series size | 160 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the 51234 model number is decoded
At 170 x 240 x 55 mm, NTN 51234 sits in the medium-section 51200 thrust family of the single-direction thrust programme. NTN builds the number from 512 is the dimension series (medium-section 51200 thrust family); 34 encodes the 170 mm bore (bore code x 5). NTN prints 261 kN axial dynamic and 835 kN axial static for this size and a 26.3 kN fatigue load limit Pu. Where misalignment between shaft and housing seats is expected, the spherical-seat washer executions (listed separately in the catalogue) absorb what the flat-seat 51234 cannot. 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
- heavy rotary furnace and kiln thrust points
- vertical hydro and pump-turbine thrust supports
- large marine winch and windlass shafts
- heavy press and mill screwdown thrust seats
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
- 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 170 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 170 mm bore.
- The C0a of 835 kN is a static rating: sizing continuous working thrust from C0a alone overstates what the raceway survives.
- The C0a of 835 kN is a static rating: sizing continuous working thrust from C0a alone overstates what the raceway survives.
- Do not reuse a thrust bearing to "absorb" shaft thermal growth — the bearing clamps axially, so growth must be handled on the radial-bearing side of the arrangement.
- The Ca 261/C0a 835 kN ratings and 26.3 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51234; 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 51234?
51234 is a single-direction thrust ball bearing to ISO 104: 170 mm shaft-washer bore, 240 mm outside diameter, 55 mm stack height (6.693 x 9.449 x 2.165 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 261 kN, C0a 835 kN and a 26.3 kN fatigue load limit Pu; the grease limiting speed is 810 r/min and the oil rating 1,200 r/min; mass about 7810 g.
How is the 51234 designation structured?
512 is the dimension series (medium-section 51200 thrust family); 34 encodes the 170 mm bore (bore code x 5). The 240 mm OD and 55 mm height follow the ISO 104 boundary plan for that series.
Can 51234 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 51234?
At the 810 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 51234?
The 170/240/55 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 261 kN / C0a 835 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.