51320 bearing: complete specifications & equivalents
The 51320 is a ISO 104 radial bearing sized 100 x 170 x 55 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 100 mm |
| Outer diameter D | 170 mm |
| Width B | 55 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 237 kN |
| Basic static load rating C0 | 595 kN |
| Fatigue load limit Pu | 23.1 kN |
| Limiting speed (mechanical) | 990 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 4880 g |
| Manufacturer designation | NTN 51320 |
| 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 | 3.937 in |
|---|---|
| Outer diameter D | 6.693 in |
| Width B | 2.165 in |
| ISO bore code | 20 |
| Radial section height (D−d)/2 | 35 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) | 15 of 25 |
| Bore above smallest 51300-series size | 75 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51320-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 51320 model number is decoded
From the heavy-section 51300 thrust family, 51320 measures 100 mm through the shaft washer, 170 mm over the outside and 55 mm in assembled height. Two fields make up the code — 513 is the dimension series (heavy-section 51300 thrust family) and 20 encodes the 100 mm bore (bore code x 5). On speed, the grease limiting speed is 990 r/min and the oil rating 1,400 r/min. The 100/170/55 envelope follows ISO 104, so dimensional interchange holds between makers — raceway osculation and ratings do not automatically follow. 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
- heavy press and forging-machine thrust seats
- ship winch and capstan thrust shafts
- crusher main-shaft thrust supports
- large rotary-table and index-table thrust rings
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
- cage breakage after repeated shock reversal banged the ball set against the pocket bridges
- cage breakage after repeated shock reversal banged the ball set against the pocket bridges
Selection pitfalls — read before you substitute
- At 100 mm bore the washers are heavy enough to sag out of square during assembly — support the stack horizontally where possible and verify face runout before loading.
- The 513 heavy section buys capacity with a larger 170 mm OD and taller stack — check the housing space before upgrading a 512 position to this series.
- Never substitute a double-direction bearing drawing part-for-part: the single-direction 51320 stack height of 55 mm and washer set differ from the double-direction execution.
- Swapping the shaft and housing washers is an easy assembly error on the 100 mm size — the bores differ only slightly, but the wrong pairing walks off-centre under load.
- 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 237/C0a 595 kN ratings and 23.1 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51320; 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 51320?
51320 is a single-direction thrust ball bearing to ISO 104: 100 mm shaft-washer bore, 170 mm outside diameter, 55 mm stack height (3.937 x 6.693 x 2.165 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 237 kN, C0a 595 kN and a 23.1 kN fatigue load limit Pu; the grease limiting speed is 990 r/min and the oil rating 1,400 r/min; mass about 4880 g.
How is the 51320 designation structured?
513 is the dimension series (heavy-section 51300 thrust family); 20 encodes the 100 mm bore (bore code x 5). The 170 mm OD and 55 mm height follow the ISO 104 boundary plan for that series.
Can 51320 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 51320?
At the 990 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 51320?
The 100/170/55 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 237 kN / C0a 595 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.