51103 bearing: complete specifications & equivalents
The 51103 is a ISO 104 radial bearing sized 17 x 30 x 9 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 17 mm |
| Outer diameter D | 30 mm |
| Width B | 9 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 10.8 kN |
| Basic static load rating C0 | 18.2 kN |
| Fatigue load limit Pu | 0.82 kN |
| Limiting speed (mechanical) | 6000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 26 g |
| Manufacturer designation | NTN 51103 |
| 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 & 51100-series range
| Bore d | 0.669 in |
|---|---|
| Outer diameter D | 1.181 in |
| Width B | 0.354 in |
| ISO bore code | 03 |
| Radial section height (D−d)/2 | 6.5 mm |
| Smallest bore in 51100-series | 10 mm |
| Largest outer diameter in 51100-series | 640 mm |
| Width range across 51100-series | 9–85 mm |
| Bore position in 51100-series (smallest first) | 4 of 46 |
| Bore above smallest 51100-series size | 7 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51103-SKF | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 17×30×9 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 51103 model number is decoded
From the light-section 51100 thrust family, 51103 measures 17 mm through the shaft washer, 30 mm over the outside and 9 mm in assembled height. Decoding 51103: 511 is the dimension series (light-section 51100 thrust family), with the bore code 03 maps to the 17 mm bore by the standard table. On speed, the grease limiting speed is 6,000 r/min and the oil rating 8,500 r/min. Against a thrust roller bearing of the same 17 mm bore, this bearing is cheaper, quieter and happier at speed, but carries far less load per mm of section. 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
- 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
- early fatigue from thrust reversal hammering the unloaded raceway, because the bearing has no contact surfaces for the opposite direction
- contamination pitting from particles settling on the horizontal housing washer — the classic failure of vertical-shaft grease-lubricated seats
- 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 17 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 511 light section is the speed-friendly end of the thrust-ball plan — for the same 17 mm bore it gives up load to gain OD, height and limiting-speed headroom.
- Below the minimum axial load the balls skid; the catalogue Ca of 10.8 kN never saves a bearing that is running too lightly loaded at 6,000 r/min.
- The C0a of 18.2 kN is a static rating: sizing continuous working thrust from C0a alone overstates what the raceway survives.
- A housing washer pressed tight in its seat cannot self-centre; the resulting eccentric running shows up as cage wear long before raceway fatigue.
- The Ca 10.8/C0a 18.2 kN ratings and 0.82 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51103; 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 51103?
51103 is a single-direction thrust ball bearing to ISO 104: 17 mm shaft-washer bore, 30 mm outside diameter, 9 mm stack height (0.669 x 1.181 x 0.354 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 10.8 kN, C0a 18.2 kN and a 0.82 kN fatigue load limit Pu; the grease limiting speed is 6,000 r/min and the oil rating 8,500 r/min; mass about 26 g.
How is the 51103 designation structured?
511 is the dimension series (light-section 51100 thrust family); the bore code 03 maps to the 17 mm bore by the standard table. The 30 mm OD and 9 mm height follow the ISO 104 boundary plan for that series.
Can 51103 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 51103?
At the 6,000 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 51103?
The 17/30/9 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 10.8 kN / C0a 18.2 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.