QJ321 bearing: complete specifications & equivalents
The QJ321 is a ISO 15 radial bearing sized 105 x 225 x 49 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 105 mm |
| Outer diameter D | 225 mm |
| Width B | 49 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | brass |
| Basic dynamic load rating C | 305 kN |
| Basic static load rating C0 | 585 kN |
| Fatigue load limit Pu | 19.6 kN |
| Limiting speed (mechanical) | 2400 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 10400 g |
| Manufacturer designation | NTN QJ321 |
| 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 | 4.134 in |
|---|---|
| Outer diameter D | 8.858 in |
| Width B | 1.929 in |
| ISO bore code | 21 |
| Radial section height (D−d)/2 | 60 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) | 19 of 28 |
| Bore above smallest QJ300-series size | 88 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| QJ321 | 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 QJ321 model number is decoded
QJ321 is the 105 mm bore member of NTN's heavy-duty QJ300 four-point family, with a 225 mm outside diameter and 49 mm section width. The designation breaks down as QJ3 is the four-point dimension series (heavy-duty QJ300 four-point family); the last two digits 21 give the bore by the standard code table (105 mm); there is no suffix — the split inner ring and 35 deg contact angle are inherent to the QJ design. NTN prints 305 kN dynamic and 585 kN static for this size and a 19.6 kN fatigue load limit Pu. If the duty is mainly high speed with modest thrust, the 7900-series cross-section is the lighter alternative; if thrust dominates, the 7300-series section carries more. Shaft and housing shoulders must clear the ring corners yet support enough face — the catalogue abutment diameters for the 105 mm bore give the working limits.
Typical equipment & failure modes
Common applications
- mining conveyor head-shaft positions
- marine auxiliary and winch gearbox shafts
- rolling-mill and metalworking drive shafts
- large pump, fan and compressor rotor 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
- machined-cage land scoring when a high-speed spindle runs past its grease rating and the cage runs dry on its guidance surface
- contamination-induced denting — hard particles rolled into the contact ellipse become the initiation points for surface fatigue
- 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
- Bearings of 105 mm bore arrive heavy enough that handling damage (dents from slings, tilting on the shaft) is a real failure precursor — use proper lifting and heating kit.
- 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.
- 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.
- 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.
- Never use a four-point or double-row bearing as a like-for-like swap for a single QJ321 without re-checking axial float, heat and housing width — the kinematics differ.
- The 305/585 kN ratings and 19.6 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for QJ321; 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 QJ321?
QJ321 is a four-point contact ball bearing to ISO 15: 105 mm bore, 225 mm outside diameter, 49 mm width (4.134 x 8.858 x 1.929 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 305 kN, C0 585 kN and a 19.6 kN fatigue load limit Pu; the grease limiting speed is 2,400 r/min and the oil rating 3,200 r/min; mass about 10400 g.
How is the QJ321 designation structured?
QJ3 is the four-point dimension series (heavy-duty QJ300 four-point family); the last two digits 21 give the bore by the standard code table (105 mm); there is no suffix — the split inner ring and 35 deg contact angle are inherent to the QJ design. The 225 mm OD and 49 mm width follow the ISO 15 boundary-dimension plan for that series.
Which axial direction does QJ321 support?
QJ321 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 QJ321?
Per NTN Ball and Roller Bearings CAT.No.2203E, the grease limiting speed is 2,400 r/min and the oil rating 3,200 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 QJ321?
The 105/225/49 mm envelope is ISO 15 interchangeable, but internal geometry — contact angle, osculation, cage and shoulder details — is maker-specific. Re-verify C 305 kN / C0 585 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.