51204 bearing: complete specifications & equivalents
The 51204 is a ISO 104 radial bearing sized 20 x 40 x 14 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 20 mm |
| Outer diameter D | 40 mm |
| Width B | 14 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 22.3 kN |
| Basic static load rating C0 | 37.5 kN |
| Fatigue load limit Pu | 1.7 kN |
| Limiting speed (mechanical) | 4100 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 81 g |
| Manufacturer designation | NTN 51204 |
| 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 | 0.787 in |
|---|---|
| Outer diameter D | 1.575 in |
| Width B | 0.551 in |
| ISO bore code | 04 |
| Radial section height (D−d)/2 | 10 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) | 5 of 39 |
| Bore above smallest 51200-series size | 10 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51204-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 51204 model number is decoded
NTN 51204 belongs to the medium-section 51200 thrust family of single-direction thrust ball bearings: 20 / 40 / 14 mm (shaft bore / OD / height). Decoding 51204: 512 is the dimension series (medium-section 51200 thrust family), with 04 encodes the 20 mm bore (bore code x 5). Catalogue mass is about 81 g for the full washer-and-cage stack. 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. 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
- small crane hook and swivel-joint thrust supports
- valve actuator and gearbox thrust seats
- food-machine vertical auger shafts
- laboratory centrifuge and mixer thrust ends
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
- washer face corrosion under long standstill in humid service, later printed into the raceway as evenly spaced pitting
Selection pitfalls — read before you substitute
- Small thrust washers of 20 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 20 mm bore.
- Swapping the shaft and housing washers is an easy assembly error on the 20 mm size — the bores differ only slightly, but the wrong pairing walks off-centre under load.
- The 4,100 r/min speed figure assumes the catalogue lubrication state; at high speed the limiting factor is often the minimum load, not the rating table.
- The 4,100 r/min speed figure assumes the catalogue lubrication state; at high speed the limiting factor is often the minimum load, not the rating table.
- The Ca 22.3/C0a 37.5 kN ratings and 1.7 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51204; 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 51204?
51204 is a single-direction thrust ball bearing to ISO 104: 20 mm shaft-washer bore, 40 mm outside diameter, 14 mm stack height (0.787 x 1.575 x 0.551 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 22.3 kN, C0a 37.5 kN and a 1.7 kN fatigue load limit Pu; the grease limiting speed is 4,100 r/min and the oil rating 5,900 r/min; mass about 81 g.
How is the 51204 designation structured?
512 is the dimension series (medium-section 51200 thrust family); 04 encodes the 20 mm bore (bore code x 5). The 40 mm OD and 14 mm height follow the ISO 104 boundary plan for that series.
Can 51204 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 51204?
At the 4,100 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 51204?
The 20/40/14 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 22.3 kN / C0a 37.5 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.