QJ308 bearing: complete specifications & equivalents
The QJ308 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 | brass |
| Basic dynamic load rating C | 67 kN |
| Basic static load rating C0 | 91.5 kN |
| Fatigue load limit Pu | 3.95 kN |
| Limiting speed (mechanical) | 6200 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 780 g |
| Manufacturer designation | NTN QJ308 |
| 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 & QJ300-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 QJ300-series | 17 mm |
| Largest outer diameter in QJ300-series | 400 mm |
| Width range across QJ300-series | 14–78 mm |
| Bore position in QJ300-series (smallest first) | 6 of 28 |
| Bore above smallest QJ300-series size | 23 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| QJ308 | 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 QJ308 model number is decoded
From the heavy-duty QJ300 four-point family, QJ308 measures 40 mm across the bore, 90 mm over the outer ring and 23 mm across the faces. Decoding QJ308: QJ3 is the four-point dimension series (heavy-duty QJ300 four-point family), with the last two digits 08 give the bore by the standard code table (40 mm); there is no suffix — the split inner ring and 35 deg contact angle are inherent to the QJ design. The radial section height here is 25.0 mm, and the catalogue couples that with C 67 kN / C0 91.5 kN. Size selection is usually finished by checking that the C0 of 91.5 kN covers the maximum static or shock condition with the catalogue safety factor, not only the running load. Mount with the thrust against the marked face: the contact angle runs from the low shoulder of the inner ring to the high shoulder of the outer ring, and reversing it throws the capacity away.
Typical equipment & failure modes
Common applications
- electric motor shafts with axial locating duty
- conveyor drive and tension-drum shafts
- agricultural gearbox and PTO shaft supports
- printing-press cylinder and folder shafts
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
- loss of preload after housing-fret or shaft creep, leaving the pair loose — ball skidding, cage rattle and a falling natural frequency follow
- resin-cage cracking on the 7900-series sizes after hot, dry running or solvent attack on the polymer
- flaking that starts at the raceway shoulder on the thrust-loaded side when axial load repeatedly exceeds the design share
- current-erosion pitting on VFD-driven motor shafts, first visible as a grey frosted band across both raceways
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 QJ split inner ring must be clamped by the shaft nut/shoulder on both halves — assembling it against a single small shoulder leaves one half-ring free to walk.
- Substituting the B (40 deg) execution for the standard 30 deg bearing changes the axial/radial load split — the shaft position and the mating bearing see different forces even though the envelope is identical.
- Substituting the B (40 deg) execution for the standard 30 deg bearing changes the axial/radial load split — the shaft position and the mating bearing see different forces even though the envelope is identical.
- A single-row angular contact left loose on the shaft to "help assembly" will fret the seat: the contact angle keeps driving the ring axially under load.
- The 67/91.5 kN ratings and 3.95 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for QJ308; 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 QJ308?
QJ308 is a four-point 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 67 kN, C0 91.5 kN and a 3.95 kN fatigue load limit Pu; the grease limiting speed is 6,200 r/min and the oil rating 8,200 r/min; mass about 780 g.
How is the QJ308 designation structured?
QJ3 is the four-point dimension series (heavy-duty QJ300 four-point family); the last two digits 08 give the bore by the standard code table (40 mm); there is no suffix — the split inner ring and 35 deg contact angle are inherent to the QJ design. The 90 mm OD and 23 mm width follow the ISO 15 boundary-dimension plan for that series.
Which axial direction does QJ308 support?
QJ308 is a four-point contact bearing: the split inner ring lets each ball touch the raceways at two points, so one bearing locates the shaft in both axial directions at its 35 deg contact angle. It is normally mounted with slight radial clearance against the housing as the axial-locating member.
What lubrication speeds does NTN print for QJ308?
Per NTN Ball and Roller Bearings CAT.No.2203E, the grease limiting speed is 6,200 r/min and the oil rating 8,200 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 QJ308?
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 67 kN / C0 91.5 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.