7308B bearing: complete specifications & equivalents
The 7308B 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 | 49.5 kN |
| Basic static load rating C0 | 30.5 kN |
| Fatigue load limit Pu | 2.37 kN |
| Limiting speed (mechanical) | 7400 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 636 g |
| Manufacturer designation | NTN 7308B |
| 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 | — |
| 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 |
|---|---|---|---|
| 7308B | 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 7308B model number is decoded
At 40 x 90 x 23 mm, NTN 7308B sits in the heavy-duty 7300 single-row family of the angular-contact programme. Two fields make up the code — 73 is the single-row dimension series (heavy-duty 7300 single-row family) and 08 encodes the 40 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). With C 49.5 kN and C0 30.5 kN, each mm of bore carries about 1.24 kN of dynamic rating. Size selection is usually finished by checking that the C0 of 30.5 kN covers the maximum static or shock condition with the catalogue safety factor, not only the running load. Shaft and housing shoulders must clear the ring corners yet support enough face — the catalogue abutment diameters for the 40 mm bore give the working limits.
Typical equipment & failure modes
Common applications
- conveyor drive and tension-drum shafts
- agricultural gearbox and PTO shaft supports
- printing-press cylinder and folder shafts
- machine-tool spindle cartridges and driven tooling
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
- machined-cage land scoring when a high-speed spindle runs past its grease rating and the cage runs dry on its guidance surface
- lubricant starvation scoring at the ball/raceway contact when grease volume or relubrication interval is guessed instead of calculated
- contamination-induced denting — hard particles rolled into the contact ellipse become the initiation points for surface fatigue
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 40 deg B-execution raises axial capacity but lowers the speed ceiling — do not copy the standard-bearing speed and preload settings onto it.
- 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.
- Do not pair two random 7308B bearings from stock and expect catalogue paired ratings — matched-set grinding is what makes DB/DF/DT preload behave, and NTN sells those as separate order numbers.
- 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 49.5/30.5 kN ratings and 2.37 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 7308B; 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 7308B?
7308B 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 49.5 kN, C0 30.5 kN and a 2.37 kN fatigue load limit Pu; the grease limiting speed is 7,400 r/min and the oil rating 9,900 r/min; mass about 636 g.
How is the 7308B 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), and the trailing B marks the 40 deg contact-angle execution (the no-letter standard bearing works at 30 deg). The 90 mm OD and 23 mm width follow the ISO 15 boundary-dimension plan for that series.
Which axial direction does 7308B support?
One 7308B 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 7308B?
Per NTN Ball and Roller Bearings CAT.No.2203E, the grease limiting speed is 7,400 r/min and the oil rating 9,900 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 7308B?
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 49.5 kN / C0 30.5 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.