QJ306 bearing: complete specifications & equivalents
The QJ306 is a ISO 15 radial bearing sized 30 x 72 x 19 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 30 mm |
| Outer diameter D | 72 mm |
| Width B | 19 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | brass |
| Basic dynamic load rating C | 44 kN |
| Basic static load rating C0 | 57.5 kN |
| Fatigue load limit Pu | 2.46 kN |
| Limiting speed (mechanical) | 8000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 420 g |
| Manufacturer designation | NTN QJ306 |
| 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 | 1.181 in |
|---|---|
| Outer diameter D | 2.835 in |
| Width B | 0.748 in |
| ISO bore code | 06 |
| Radial section height (D−d)/2 | 21 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) | 4 of 28 |
| Bore above smallest QJ300-series size | 13 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| QJ306 | 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 QJ306 model number is decoded
At 30 x 72 x 19 mm, NTN QJ306 sits in the heavy-duty QJ300 four-point family of the angular-contact programme. Reading the code: QJ3 is the four-point dimension series (heavy-duty QJ300 four-point family), the last two digits 06 give the bore by the standard code table (30 mm); there is no suffix — the split inner ring and 35 deg contact angle are inherent to the QJ design. Because the contact line is angled, one bearing of this type takes radial load plus thrust from one direction only — the opposite direction needs a second bearing or a matched set. Selection starts from the thrust share: as axial load grows past roughly half the radial load, an angular-contact position of this section usually outlives a deep-groove one. Shaft and housing shoulders must clear the ring corners yet support enough face — the catalogue abutment diameters for the 30 mm bore give the working limits.
Typical equipment & failure modes
Common applications
- printing-press cylinder and folder shafts
- machine-tool spindle cartridges and driven tooling
- industrial pump and blower impeller shafts
- gearbox input shafts under helical-gear thrust
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
- machined-cage land scoring when a high-speed spindle runs past its grease rating and the cage runs dry on its guidance surface
- current-erosion pitting on VFD-driven motor shafts, first visible as a grey frosted band across both raceways
- 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 30 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.
- 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.
- A QJ306 mounted the wrong way round still turns smoothly by hand; the failure shows up weeks later as raceway flaking on the unloaded-looking side.
- The 8,000 r/min speed figure assumes the catalogue lubrication state and a correctly set pair; real limits drop fast with excess grease fill or heavy preload.
- The 44/57.5 kN ratings and 2.46 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for QJ306; 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 QJ306?
QJ306 is a four-point contact ball bearing to ISO 15: 30 mm bore, 72 mm outside diameter, 19 mm width (1.181 x 2.835 x 0.748 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 44 kN, C0 57.5 kN and a 2.46 kN fatigue load limit Pu; the grease limiting speed is 8,000 r/min and the oil rating 11,000 r/min; mass about 420 g.
How is the QJ306 designation structured?
QJ3 is the four-point dimension series (heavy-duty QJ300 four-point family); the last two digits 06 give the bore by the standard code table (30 mm); there is no suffix — the split inner ring and 35 deg contact angle are inherent to the QJ design. The 72 mm OD and 19 mm width follow the ISO 15 boundary-dimension plan for that series.
Which axial direction does QJ306 support?
QJ306 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 QJ306?
Per NTN Ball and Roller Bearings CAT.No.2203E, the grease limiting speed is 8,000 r/min and the oil rating 11,000 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 QJ306?
The 30/72/19 mm envelope is ISO 15 interchangeable, but internal geometry — contact angle, osculation, cage and shoulder details — is maker-specific. Re-verify C 44 kN / C0 57.5 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.