7308-NTN bearing: complete specifications & equivalents
The 7308-NTN is a ISO 15 radial bearing sized 40 x 90 x 23 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 40 mm |
| Outer diameter D | 90 mm |
| Width B | 23 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 54 kN |
| Basic static load rating C0 | 33 kN |
| Fatigue load limit Pu | 2.58 kN |
| Limiting speed (mechanical) | 8600 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 625 g |
| Manufacturer designation | NTN 7308 |
| 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 | 1.575 in |
|---|---|
| Outer diameter D | 3.543 in |
| Width B | 0.906 in |
| ISO bore code | 08 |
| Radial section height (D−d)/2 | 25 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) | 9 of 32 |
| Bore above smallest 7300-series size | 30 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 7308 | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×90×23 mm envelope per ISO 15; catalogue load ratings differ by >10% — re-rate the application before substituting. |
| 7308-ACCBM | 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. |
| 7308-BE-2RZP | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×90×23 mm envelope per ISO 15; seal variant (OPEN vs RSR) and load ratings differ — confirm sealing and rating before substituting. |
| 7308-BECBM | 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. |
| 7308-BECBP | 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. |
| 7308-BECBY | 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. |
| 7308-BEGAPH | 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. |
| 7308-BEP | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×90×23 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 7308-NTN model number is decoded
From the heavy-duty 7300 single-row family, 7308 measures 40 mm across the bore, 90 mm over the outer ring and 23 mm across the faces. Reading the code: 73 is the single-row dimension series (heavy-duty 7300 single-row family), 08 encodes the 40 mm bore (bore code x 5); with no letter after the digits it is the standard 30 deg contact-angle execution — the 40 deg version carries a B. With C 54 kN and C0 33 kN, each mm of bore carries about 1.35 kN of dynamic rating. Size selection is usually finished by checking that the C0 of 33 kN covers the maximum static or shock condition with the catalogue safety factor, not only the running load. 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
- gearbox input shafts under helical-gear thrust
- electric motor shafts with axial locating duty
- conveyor drive and tension-drum shafts
- agricultural gearbox and PTO shaft supports
Known failure patterns
- false brinelling on the raceway contact ellipses when a preloaded spindle sits vibrating at standstill — visible as evenly spaced flute-like wear at ball pitch
- 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
- edge loading and early spalling from housing bores that are out of round or shoulders that are too small for the ring face
- edge loading and early spalling from housing bores that are out of round or shoulders that are too small for the ring face
Selection pitfalls — read before you substitute
- In this size class the common miss is lubrication interval, not fit — a 40 mm spindle at the catalogue speeds needs a calculated relubrication plan, not a calendar one.
- The standard 30 deg bearing and its B (40 deg) sibling share the envelope; picking between them is a load-direction decision, not a quality upgrade.
- The C0 of 33 kN is a static rating, not a permissible running thrust — sizing continuous axial load from C0 alone is a recurring drawing-office error.
- Never use a four-point or double-row bearing as a like-for-like swap for a single 7308 without re-checking axial float, heat and housing width — the kinematics differ.
- On a 40 mm shaft, an interference fit eats internal clearance; skipping the clearance/preload recalculation is the classic cause of a new bearing running 20 deg C hotter than the drawing suggests.
- The 54/33 kN ratings and 2.58 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 7308; 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 7308?
7308 is a single-row angular contact ball bearing to ISO 15: 40 mm bore, 90 mm outside diameter, 23 mm width (1.575 x 3.543 x 0.906 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 54 kN, C0 33 kN and a 2.58 kN fatigue load limit Pu; the grease limiting speed is 8,600 r/min and the oil rating 12,000 r/min; mass about 625 g.
How is the 7308 designation structured?
73 is the single-row dimension series (heavy-duty 7300 single-row family); 08 encodes the 40 mm bore (bore code x 5); with no letter after the digits it is the standard 30 deg contact-angle execution — the 40 deg version carries a B. The 90 mm OD and 23 mm width follow the ISO 15 boundary-dimension plan for that series.
Which axial direction does 7308 support?
One 7308 alone takes thrust in one direction only, along its 30 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 7308?
Per NTN Ball and Roller Bearings CAT.No.2203E, the grease limiting speed is 8,600 r/min and the oil rating 12,000 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 7308?
The 40/90/23 mm envelope is ISO 15 interchangeable, but internal geometry — contact angle, osculation, cage and shoulder details — is maker-specific. Re-verify C 54 kN / C0 33 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.