51309 bearing: complete specifications & equivalents
The 51309 is a ISO 104 radial bearing sized 45 x 85 x 28 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 45 mm |
| Outer diameter D | 85 mm |
| Width B | 28 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 80 kN |
| Basic static load rating C0 | 163 kN |
| Fatigue load limit Pu | 7.35 kN |
| Limiting speed (mechanical) | 2000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 684 g |
| Manufacturer designation | NTN 51309 |
| 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 | 1.772 in |
|---|---|
| Outer diameter D | 3.346 in |
| Width B | 1.102 in |
| ISO bore code | 09 |
| Radial section height (D−d)/2 | 20 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) | 5 of 25 |
| Bore above smallest 51300-series size | 20 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51309-SKF | SKF | full Dimensions and internal design equivalent — standard interchange. | Identical ISO 15 envelope, seal and ratings band — standard interchange; re-verify precision class and clearance per supplier. |
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 51309 model number is decoded
NTN 51309 belongs to the heavy-section 51300 thrust family of single-direction thrust ball bearings: 45 / 85 / 28 mm (shaft bore / OD / height). Two fields make up the code — 513 is the dimension series (heavy-section 51300 thrust family) and 09 encodes the 45 mm bore (bore code x 5). The static margin, C0a 163 kN against Ca 80 kN, is what carries slow oscillating or shock thrust without permanent raceway dents. Where misalignment between shaft and housing seats is expected, the spherical-seat washer executions (listed separately in the catalogue) absorb what the flat-seat 51309 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
- press and punch-machine thrust seats
- conveyor vertical-drive thrust positions
- vertical motor and pump thrust shoes
- machine-tool tailstock and steady-rest screws
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
- contamination pitting from particles settling on the horizontal housing washer — the classic failure of vertical-shaft grease-lubricated seats
- cage breakage after repeated shock reversal banged the ball set against the pocket bridges
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 45 mm size together from unpacking to assembly.
- The 513 heavy section buys capacity with a larger 85 mm OD and taller stack — check the housing space before upgrading a 512 position to this series.
- Radial load is the silent killer here: a belt pull or gear force on the same shaft must land on a radial bearing, because 51309 has no radial capacity at all.
- Swapping the shaft and housing washers is an easy assembly error on the 45 mm size — the bores differ only slightly, but the wrong pairing walks off-centre under load.
- Shock thrust above C0a 163 kN leaves dents that later become fatigue origins — crane-hook and press applications need the static check, not just the life calculation.
- The Ca 80/C0a 163 kN ratings and 7.35 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51309; 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 51309?
51309 is a single-direction thrust ball bearing to ISO 104: 45 mm shaft-washer bore, 85 mm outside diameter, 28 mm stack height (1.772 x 3.346 x 1.102 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 80 kN, C0a 163 kN and a 7.35 kN fatigue load limit Pu; the grease limiting speed is 2,000 r/min and the oil rating 2,900 r/min; mass about 684 g.
How is the 51309 designation structured?
513 is the dimension series (heavy-section 51300 thrust family); 09 encodes the 45 mm bore (bore code x 5). The 85 mm OD and 28 mm height follow the ISO 104 boundary plan for that series.
Can 51309 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 51309?
At the 2,000 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 51309?
The 45/85/28 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 80 kN / C0a 163 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.