51168 bearing: complete specifications & equivalents
The 51168 is a ISO 104 radial bearing sized 340 x 420 x 64 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 340 mm |
| Outer diameter D | 420 mm |
| Width B | 64 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 375 kN |
| Basic static load rating C0 | 1760 kN |
| Fatigue load limit Pu | 40.5 kN |
| Limiting speed (mechanical) | 530 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 19700 g |
| Manufacturer designation | NTN 51168 |
| 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 | 13.386 in |
|---|---|
| Outer diameter D | 16.535 in |
| Width B | 2.52 in |
| ISO bore code | 68 |
| Radial section height (D−d)/2 | 40 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) | 37 of 46 |
| Bore above smallest 51100-series size | 330 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the 51168 model number is decoded
In NTN Ball and Roller Bearings CAT.No.2203E, 51168 appears as a light-section 51100 thrust family bearing with a 340 mm shaft washer, a 420 mm housing diameter and 64 mm of stack height. The designation is 511 is the dimension series (light-section 51100 thrust family) plus 68 encodes the 340 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. Where misalignment between shaft and housing seats is expected, the spherical-seat washer executions (listed separately in the catalogue) absorb what the flat-seat 51168 cannot. Preload or working clearance must guarantee the minimum axial load at the catalogue speed; a spring or dead-weight arrangement is the usual answer on high-speed vertical shafts.
Typical equipment & failure modes
Common applications
- large mixer and reactor vertical shafts
- bulk-handler stacker/reclaimer thrust pivots
- heavy rotary furnace and kiln thrust points
- vertical hydro and pump-turbine thrust supports
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
- edge loading from a shaft washer mounted off-centre, cutting the contact ellipse short at one side of the track
- 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 340 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 340 mm bore it gives up load to gain OD, height and limiting-speed headroom.
- The C0a of 1760 kN is a static rating: sizing continuous working thrust from C0a alone overstates what the raceway survives.
- The C0a of 1760 kN is a static rating: sizing continuous working thrust from C0a alone overstates what the raceway survives.
- Single-direction means exactly that: thrust on 51168 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 375/C0a 1760 kN ratings and 40.5 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51168; 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 51168?
51168 is a single-direction thrust ball bearing to ISO 104: 340 mm shaft-washer bore, 420 mm outside diameter, 64 mm stack height (13.386 x 16.535 x 2.52 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 375 kN, C0a 1760 kN and a 40.5 kN fatigue load limit Pu; the grease limiting speed is 530 r/min and the oil rating 760 r/min; mass about 19700 g.
How is the 51168 designation structured?
511 is the dimension series (light-section 51100 thrust family); 68 encodes the 340 mm bore (bore code x 5). The 420 mm OD and 64 mm height follow the ISO 104 boundary plan for that series.
Can 51168 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 51168?
At the 530 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 51168?
The 340/420/64 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 375 kN / C0a 1760 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.