7311B bearing: complete specifications & equivalents
The 7311B is a ISO 15 radial bearing sized 55 x 120 x 29 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 55 mm |
| Outer diameter D | 120 mm |
| Width B | 29 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 87 kN |
| Basic static load rating C0 | 56.5 kN |
| Fatigue load limit Pu | 4.45 kN |
| Limiting speed (mechanical) | 5500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1420 g |
| Manufacturer designation | NTN 7311B |
| Standard | ISO 15 |
| 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 & 7300-series range
| Bore d | 2.165 in |
|---|---|
| Outer diameter D | 4.724 in |
| Width B | 1.142 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 32.5 mm |
| Smallest bore in 7300-series | 10 mm |
| Largest outer diameter in 7300-series | 420 mm |
| Width range across 7300-series | 11–80 mm |
| Bore position in 7300-series (smallest first) | 12 of 32 |
| Bore above smallest 7300-series size | 45 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 7311B | ISO 15 | full Dimensions and internal design equivalent — standard interchange. | ISO 15 boundary-dimension envelope; standard interchange — confirm clearance class and precision with the 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 7311B model number is decoded
From the heavy-duty 7300 single-row family, 7311B measures 55 mm across the bore, 120 mm over the outer ring and 29 mm across the faces. The designation breaks down as 73 is the single-row dimension series (heavy-duty 7300 single-row family); 11 encodes the 55 mm bore (bore code x 5), and the trailing B marks the 40 deg contact-angle execution (the no-letter standard bearing works at 30 deg). At roughly 32.5 mm of radial section, the catalogue still quotes 87 kN dynamic capacity for the 55 mm bore. Against a deep-groove bearing of the same 55 mm bore, this bearing trades some pure-radial comfort for real one-direction thrust capacity and higher running accuracy. Set preload or end-play with the pair as a unit and lock the adjustment; a single angular-contact bearing cannot run free like a deep-groove one.
Typical equipment & failure modes
Common applications
- industrial pump and blower impeller shafts
- gearbox input shafts under helical-gear thrust
- electric motor shafts with axial locating duty
- conveyor drive and tension-drum shafts
Known failure patterns
- impact brinelling dents on the 30 deg contact path after a shaft-side hammer blow during mounting, because axial shock travels straight through the contact angle
- thermal runaway from excessive preload: the pair runs hot, grease darkens and the contact ellipse spreads until the raceways smear
- pressed-steel cage pocket wear and rivet loosening after repeated ball skid at light load and high speed
- flaking that starts at the raceway shoulder on the thrust-loaded side when axial load repeatedly exceeds the design share
- lubricant starvation scoring at the ball/raceway contact when grease volume or relubrication interval is guessed instead of calculated
Selection pitfalls — read before you substitute
- In this size class the common miss is lubrication interval, not fit — a 55 mm spindle at the catalogue speeds needs a calculated relubrication plan, not a calendar one.
- The 40 deg B-execution raises axial capacity but lowers the speed ceiling — do not copy the standard-bearing speed and preload settings onto it.
- The C0 of 56.5 kN is a static rating, not a permissible running thrust — sizing continuous axial load from C0 alone is a recurring drawing-office error.
- If the application vibrates at standstill (transport, idle machine next to a running line), specify protection: the contact ellipse of a preloaded bearing false-brinells faster than a loose one.
- Catalogue mass and ratings belong to the open execution; shields, seals and resin cages change both the speed ceiling and the thermal behaviour of the same basic size.
- The 87/56.5 kN ratings and 4.45 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 7311B; internal geometry legitimately differs between manufacturers, so re-verify ratings, contact angle and suffix before substituting another make on a rated drive.
Frequently asked questions
What are the dimensions and catalogue ratings of NTN 7311B?
7311B is a single-row angular contact ball bearing to ISO 15: 55 mm bore, 120 mm outside diameter, 29 mm width (2.165 x 4.724 x 1.142 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 87 kN, C0 56.5 kN and a 4.45 kN fatigue load limit Pu; the grease limiting speed is 5,500 r/min and the oil rating 7,300 r/min; mass about 1420 g.
How is the 7311B designation structured?
73 is the single-row dimension series (heavy-duty 7300 single-row family); 11 encodes the 55 mm bore (bore code x 5), and the trailing B marks the 40 deg contact-angle execution (the no-letter standard bearing works at 30 deg). The 120 mm OD and 29 mm width follow the ISO 15 boundary-dimension plan for that series.
Which axial direction does 7311B support?
One 7311B alone takes thrust in one direction only, along its 40 deg contact angle; reversing thrust calls for a second bearing or a factory-matched DB/DF/DT pair (the catalogue right-hand columns list the paired ratings). Radial load is always carried as a combined load through the angled contact.
What lubrication speeds does NTN print for 7311B?
Per NTN Ball and Roller Bearings CAT.No.2203E, the grease limiting speed is 5,500 r/min and the oil rating 7,300 r/min. These are catalogue ceilings for a correctly mounted bearing with the stated lubricant; preload, fill quantity, ambient heat and paired arrangements all move the real limit.
What should be checked before substituting another make for 7311B?
The 55/120/29 mm envelope is ISO 15 interchangeable, but internal geometry — contact angle, osculation, cage and shoulder details — is maker-specific. Re-verify C 87 kN / C0 56.5 kN, the speed figures, contact angle and suffix meaning against the donor catalogue before swapping on a rated drive.
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.