51306 bearing: complete specifications & equivalents
The 51306 is a ISO 104 radial bearing sized 30 x 60 x 21 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 30 mm |
| Outer diameter D | 60 mm |
| Width B | 21 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 43 kN |
| Basic static load rating C0 | 78.5 kN |
| Fatigue load limit Pu | 3.55 kN |
| Limiting speed (mechanical) | 2800 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 269 g |
| Manufacturer designation | NTN 51306 |
| 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 | 1.181 in |
|---|---|
| Outer diameter D | 2.362 in |
| Width B | 0.827 in |
| ISO bore code | 06 |
| Radial section height (D−d)/2 | 15 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) | 2 of 25 |
| Bore above smallest 51300-series size | 5 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51306-SKF | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 30×60×21 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 51306 model number is decoded
From the heavy-section 51300 thrust family, 51306 measures 30 mm through the shaft washer, 60 mm over the outside and 21 mm in assembled height. NTN builds the number from 513 is the dimension series (heavy-section 51300 thrust family); 06 encodes the 30 mm bore (bore code x 5). Flat-seat washers make the bearing tolerant of simple housings but demand square faces: the whole 43 kN rating assumes the load arrives truly axial. Selection starts from the load direction: if thrust ever reverses, plan a second thrust bearing (or a double-direction execution) rather than relying on the unloaded raceway. On a vertical shaft, pack grease between the washers and plan a relubrication path — centrifugal effect drives grease outward and the track runs dry without it.
Typical equipment & failure modes
Common applications
- conveyor vertical-drive thrust positions
- vertical motor and pump thrust shoes
- machine-tool tailstock and steady-rest screws
- medium crane hook blocks and slewing jibs
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
- lubricant starvation scoring on the raceway track when grease is thrown outward by centrifugal effect and never replaced
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 30 mm size together from unpacking to assembly.
- The 513 heavy section buys capacity with a larger 60 mm OD and taller stack — check the housing space before upgrading a 512 position to this series.
- 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.
- Single-direction means exactly that: thrust on 51306 in the wrong direction separates the washers and drops the ball set — if reversal is possible even during coast-down, engineer against it.
- Never substitute a double-direction bearing drawing part-for-part: the single-direction 51306 stack height of 21 mm and washer set differ from the double-direction execution.
- The Ca 43/C0a 78.5 kN ratings and 3.55 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51306; 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 51306?
51306 is a single-direction thrust ball bearing to ISO 104: 30 mm shaft-washer bore, 60 mm outside diameter, 21 mm stack height (1.181 x 2.362 x 0.827 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 43 kN, C0a 78.5 kN and a 3.55 kN fatigue load limit Pu; the grease limiting speed is 2,800 r/min and the oil rating 3,900 r/min; mass about 269 g.
How is the 51306 designation structured?
513 is the dimension series (heavy-section 51300 thrust family); 06 encodes the 30 mm bore (bore code x 5). The 60 mm OD and 21 mm height follow the ISO 104 boundary plan for that series.
Can 51306 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 51306?
At the 2,800 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 51306?
The 30/60/21 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 43 kN / C0a 78.5 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.