51205 bearing: complete specifications & equivalents
The 51205 is a ISO 104 radial bearing sized 25 x 47 x 15 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 25 mm |
| Outer diameter D | 47 mm |
| Width B | 15 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 27.8 kN |
| Basic static load rating C0 | 50.5 kN |
| Fatigue load limit Pu | 2.28 kN |
| Limiting speed (mechanical) | 3700 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 111 g |
| Manufacturer designation | NTN 51205 |
| 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 | 0.984 in |
|---|---|
| Outer diameter D | 1.85 in |
| Width B | 0.591 in |
| ISO bore code | 05 |
| Radial section height (D−d)/2 | 11 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) | 6 of 39 |
| Bore above smallest 51200-series size | 15 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51205-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 51205 model number is decoded
The medium-section 51200 thrust family entry 51205 stacks a shaft washer, ball-and-cage set and housing washer into 15 mm of height over a 25 mm bore. NTN builds the number from 512 is the dimension series (medium-section 51200 thrust family); 05 encodes the 25 mm bore (bore code x 5). With Ca 27.8 kN and C0a 50.5 kN, each mm of shaft bore carries about 1.11 kN of dynamic axial rating. Choose the medium-section 51200 thrust family when the shaft carries pure thrust in one direction at moderate speed — vertical shafts are the textbook case. 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
- food-machine vertical auger shafts
- laboratory centrifuge and mixer thrust ends
- small vertical pump and agitator thrust positions
- bench drill-press and tapping-machine spindles
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
- lubricant starvation scoring on the raceway track when grease is thrown outward by centrifugal effect and never replaced
Selection pitfalls — read before you substitute
- Small thrust washers of 25 mm bore bend if the shaft shoulder is rough — check burrs before seating, and never press on the housing washer to drive the shaft washer home.
- The 512 medium section is the default choice: balanced height and capacity for general vertical-shaft duty at 25 mm bore.
- The C0a of 50.5 kN is a static rating: sizing continuous working thrust from C0a alone overstates what the raceway survives.
- Shock thrust above C0a 50.5 kN leaves dents that later become fatigue origins — crane-hook and press applications need the static check, not just the life calculation.
- 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 27.8/C0a 50.5 kN ratings and 2.28 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51205; 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 51205?
51205 is a single-direction thrust ball bearing to ISO 104: 25 mm shaft-washer bore, 47 mm outside diameter, 15 mm stack height (0.984 x 1.85 x 0.591 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 27.8 kN, C0a 50.5 kN and a 2.28 kN fatigue load limit Pu; the grease limiting speed is 3,700 r/min and the oil rating 5,300 r/min; mass about 111 g.
How is the 51205 designation structured?
512 is the dimension series (medium-section 51200 thrust family); 05 encodes the 25 mm bore (bore code x 5). The 47 mm OD and 15 mm height follow the ISO 104 boundary plan for that series.
Can 51205 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 51205?
At the 3,700 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 51205?
The 25/47/15 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 27.8 kN / C0a 50.5 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.