51308 bearing: complete specifications & equivalents
The 51308 is a ISO 104 radial bearing sized 40 x 78 x 26 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 40 mm |
| Outer diameter D | 78 mm |
| Width B | 26 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 69 kN |
| Basic static load rating C0 | 135 kN |
| Fatigue load limit Pu | 6.05 kN |
| Limiting speed (mechanical) | 2200 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 548 g |
| Manufacturer designation | NTN 51308 |
| 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 & 51300-series range
| Bore d | 1.575 in |
|---|---|
| Outer diameter D | 3.071 in |
| Width B | 1.024 in |
| ISO bore code | 08 |
| Radial section height (D−d)/2 | 19 mm |
| Smallest bore in 51300-series | 25 mm |
| Largest outer diameter in 51300-series | 340 mm |
| Width range across 51300-series | 18–110 mm |
| Bore position in 51300-series (smallest first) | 4 of 25 |
| Bore above smallest 51300-series size | 15 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51308-SKF | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×78×26 mm envelope per ISO 15; catalogue load ratings differ by >10% — re-rate the application before substituting. |
Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.
How the 51308 model number is decoded
In NTN Ball and Roller Bearings CAT.No.2203E, 51308 appears as a heavy-section 51300 thrust family bearing with a 40 mm shaft washer, a 78 mm housing diameter and 26 mm of stack height. Reading the code: 513 is the dimension series (heavy-section 51300 thrust family), and 08 encodes the 40 mm bore (bore code x 5). At 26 mm of height the stack is compact for the 40 mm bore class, trading section height for the heavy-section load level. The 40/78/26 envelope follows ISO 104, so dimensional interchange holds between makers — raceway osculation and ratings do not automatically follow. 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
- extruder and mixer thrust housings
- winch and capstan vertical shafts
- press and punch-machine thrust seats
- conveyor vertical-drive 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
- cage breakage after repeated shock reversal banged the ball set against the pocket bridges
- edge loading from a shaft washer mounted off-centre, cutting the contact ellipse short at one side of the track
Selection pitfalls — read before you substitute
- In this size class the frequent miss is washer identification: keep the catalogued shaft/housing washer pairing of the 40 mm size together from unpacking to assembly.
- The 513 heavy section buys capacity with a larger 78 mm OD and taller stack — check the housing space before upgrading a 512 position to this series.
- Never substitute a double-direction bearing drawing part-for-part: the single-direction 51308 stack height of 26 mm and washer set differ from the double-direction execution.
- Below the minimum axial load the balls skid; the catalogue Ca of 69 kN never saves a bearing that is running too lightly loaded at 2,200 r/min.
- Below the minimum axial load the balls skid; the catalogue Ca of 69 kN never saves a bearing that is running too lightly loaded at 2,200 r/min.
- The Ca 69/C0a 135 kN ratings and 6.05 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51308; 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 51308?
51308 is a single-direction thrust ball bearing to ISO 104: 40 mm shaft-washer bore, 78 mm outside diameter, 26 mm stack height (1.575 x 3.071 x 1.024 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 69 kN, C0a 135 kN and a 6.05 kN fatigue load limit Pu; the grease limiting speed is 2,200 r/min and the oil rating 3,100 r/min; mass about 548 g.
How is the 51308 designation structured?
513 is the dimension series (heavy-section 51300 thrust family); 08 encodes the 40 mm bore (bore code x 5). The 78 mm OD and 26 mm height follow the ISO 104 boundary plan for that series.
Can 51308 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 51308?
At the 2,200 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 51308?
The 40/78/26 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 69 kN / C0a 135 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.