51217 bearing: complete specifications & equivalents
The 51217 is a ISO 104 radial bearing sized 85 x 125 x 31 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 85 mm |
| Outer diameter D | 125 mm |
| Width B | 31 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 95.5 kN |
| Basic static load rating C0 | 264 kN |
| Fatigue load limit Pu | 11.6 kN |
| Limiting speed (mechanical) | 1600 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1250 g |
| Manufacturer designation | NTN 51217 |
| 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 | 3.346 in |
|---|---|
| Outer diameter D | 4.921 in |
| Width B | 1.22 in |
| ISO bore code | 17 |
| Radial section height (D−d)/2 | 20 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) | 18 of 39 |
| Bore above smallest 51200-series size | 75 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51217-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 51217 model number is decoded
In NTN Ball and Roller Bearings CAT.No.2203E, 51217 appears as a medium-section 51200 thrust family bearing with a 85 mm shaft washer, a 125 mm housing diameter and 31 mm of stack height. Decoding 51217: 512 is the dimension series (medium-section 51200 thrust family), with 17 encodes the 85 mm bore (bore code x 5). Flat-seat washers make the bearing tolerant of simple housings but demand square faces: the whole 95.5 kN rating assumes the load arrives truly axial. Size selection ends with the minimum-load check: at the 1,600 r/min class speed, the balls need a defined axial preload to keep rolling instead of skidding. 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
- 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
- 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
- cage breakage after repeated shock reversal banged the ball set against the pocket bridges
- washer face corrosion under long standstill in humid service, later printed into the raceway as evenly spaced pitting
Selection pitfalls — read before you substitute
- At 85 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 512 medium section is the default choice: balanced height and capacity for general vertical-shaft duty at 85 mm bore.
- Do not reuse a thrust bearing to "absorb" shaft thermal growth — the bearing clamps axially, so growth must be handled on the radial-bearing side of the arrangement.
- Never substitute a double-direction bearing drawing part-for-part: the single-direction 51217 stack height of 31 mm and washer set differ from the double-direction execution.
- Never substitute a double-direction bearing drawing part-for-part: the single-direction 51217 stack height of 31 mm and washer set differ from the double-direction execution.
- The Ca 95.5/C0a 264 kN ratings and 11.6 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51217; 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 51217?
51217 is a single-direction thrust ball bearing to ISO 104: 85 mm shaft-washer bore, 125 mm outside diameter, 31 mm stack height (3.346 x 4.921 x 1.22 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 95.5 kN, C0a 264 kN and a 11.6 kN fatigue load limit Pu; the grease limiting speed is 1,600 r/min and the oil rating 2,200 r/min; mass about 1250 g.
How is the 51217 designation structured?
512 is the dimension series (medium-section 51200 thrust family); 17 encodes the 85 mm bore (bore code x 5). The 125 mm OD and 31 mm height follow the ISO 104 boundary plan for that series.
Can 51217 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 51217?
At the 1,600 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 51217?
The 85/125/31 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 95.5 kN / C0a 264 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.