51238 bearing: complete specifications & equivalents
The 51238 is a ISO 104 radial bearing sized 190 x 270 x 62 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 190 mm |
| Outer diameter D | 270 mm |
| Width B | 62 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 310 kN |
| Basic static load rating C0 | 1060 kN |
| Fatigue load limit Pu | 31.5 kN |
| Limiting speed (mechanical) | 710 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 11300 g |
| Manufacturer designation | NTN 51238 |
| 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 | 7.48 in |
|---|---|
| Outer diameter D | 10.63 in |
| Width B | 2.441 in |
| ISO bore code | 38 |
| Radial section height (D−d)/2 | 40 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) | 29 of 39 |
| Bore above smallest 51200-series size | 180 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the 51238 model number is decoded
In NTN Ball and Roller Bearings CAT.No.2203E, 51238 appears as a medium-section 51200 thrust family bearing with a 190 mm shaft washer, a 270 mm housing diameter and 62 mm of stack height. Decoding 51238: 512 is the dimension series (medium-section 51200 thrust family), with 38 encodes the 190 mm bore (bore code x 5). The ball-and-cage set is separable from both washers, which is why the mounting order (shaft washer first, then cage, then housing washer) matters. Size selection ends with the minimum-load check: at the 710 r/min class speed, the balls need a defined axial preload to keep rolling instead of skidding. Mount the stack in order and confirm the shaft washer sits against its shoulder before loading: pressing through the balls brinells the raceway on the spot.
Typical equipment & failure modes
Common applications
- vertical hydro and pump-turbine thrust supports
- large marine winch and windlass shafts
- heavy press and mill screwdown thrust seats
- crane slew-ring auxiliary thrust positions
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
- lubricant starvation scoring on the raceway track when grease is thrown outward by centrifugal effect and never replaced
- washer face corrosion under long standstill in humid service, later printed into the raceway as evenly spaced pitting
Selection pitfalls — read before you substitute
- For a 190 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 190 mm bore.
- Below the minimum axial load the balls skid; the catalogue Ca of 310 kN never saves a bearing that is running too lightly loaded at 710 r/min.
- Shock thrust above C0a 1060 kN leaves dents that later become fatigue origins — crane-hook and press applications need the static check, not just the life calculation.
- Radial load is the silent killer here: a belt pull or gear force on the same shaft must land on a radial bearing, because 51238 has no radial capacity at all.
- The Ca 310/C0a 1060 kN ratings and 31.5 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51238; 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 51238?
51238 is a single-direction thrust ball bearing to ISO 104: 190 mm shaft-washer bore, 270 mm outside diameter, 62 mm stack height (7.48 x 10.63 x 2.441 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 310 kN, C0a 1060 kN and a 31.5 kN fatigue load limit Pu; the grease limiting speed is 710 r/min and the oil rating 1,000 r/min; mass about 11300 g.
How is the 51238 designation structured?
512 is the dimension series (medium-section 51200 thrust family); 38 encodes the 190 mm bore (bore code x 5). The 270 mm OD and 62 mm height follow the ISO 104 boundary plan for that series.
Can 51238 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 51238?
At the 710 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 51238?
The 190/270/62 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 310 kN / C0a 1060 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.