51248 bearing: complete specifications & equivalents
The 51248 is a ISO 104 radial bearing sized 240 x 340 x 78 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 240 mm |
| Outer diameter D | 340 mm |
| Width B | 78 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 415 kN |
| Basic static load rating C0 | 1650 kN |
| Fatigue load limit Pu | 44 kN |
| Limiting speed (mechanical) | 550 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 22400 g |
| Manufacturer designation | NTN 51248 |
| 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 | 9.449 in |
|---|---|
| Outer diameter D | 13.386 in |
| Width B | 3.071 in |
| ISO bore code | 48 |
| 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) | 32 of 39 |
| Bore above smallest 51200-series size | 230 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the 51248 model number is decoded
At 240 x 340 x 78 mm, NTN 51248 sits in the medium-section 51200 thrust family of the single-direction thrust programme. The designation is 512 is the dimension series (medium-section 51200 thrust family) plus 48 encodes the 240 mm bore (bore code x 5). With Ca 415 kN and C0a 1650 kN, each mm of shaft bore carries about 1.73 kN of dynamic axial rating. The 240/340/78 envelope follows ISO 104, so dimensional interchange holds between makers — raceway osculation and ratings do not automatically follow. After assembly, rotate under light load and check torque and temperature rise — a thrust ball bearing mounted with the washers swapped runs, but fails fast.
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
- cage pocket wear and ball skid polish after long running below the minimum axial load, the balls sliding instead of rolling on the washers
- housing-washer rocking on an out-of-square support face, seen as uneven wear around the raceway circle and rising running torque
- rapid flaking after radial load was allowed onto the bearing — a single-direction thrust ball bearing carries axial load only
- 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 240 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 240 mm bore.
- Never substitute a double-direction bearing drawing part-for-part: the single-direction 51248 stack height of 78 mm and washer set differ from the double-direction execution.
- The 550 r/min speed figure assumes the catalogue lubrication state; at high speed the limiting factor is often the minimum load, not the rating table.
- 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 415/C0a 1650 kN ratings and 44 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51248; 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 51248?
51248 is a single-direction thrust ball bearing to ISO 104: 240 mm shaft-washer bore, 340 mm outside diameter, 78 mm stack height (9.449 x 13.386 x 3.071 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 415 kN, C0a 1650 kN and a 44 kN fatigue load limit Pu; the grease limiting speed is 550 r/min and the oil rating 790 r/min; mass about 22400 g.
How is the 51248 designation structured?
512 is the dimension series (medium-section 51200 thrust family); 48 encodes the 240 mm bore (bore code x 5). The 340 mm OD and 78 mm height follow the ISO 104 boundary plan for that series.
Can 51248 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 51248?
At the 550 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 51248?
The 240/340/78 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 415 kN / C0a 1650 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.