QJ-306-N2MA bearing: complete specifications & equivalents
The QJ-306-N2MA 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 | SKF |
| 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 | 53 kN |
| Basic static load rating C0 | 41.5 kN |
| Fatigue load limit Pu | 1.76 kN |
| Limiting speed (mechanical) | 17000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 420 g |
| Manufacturer designation | QJ 306 N2MA |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018) |
| Last verified | 2026-09-27 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018)) · extracted 2026-09-27
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018)); SKF® and SKF Explorer® are trademarks of AB SKF, used here for identification only — mpnbase is not an authorized SKF distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at skf.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 | — |
| 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 27 |
| Bore above smallest QJ300-series size | 13 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 7306-BE-2RZP | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 30×72×19 mm envelope, but catalogue C/C0 differ between executions (53/41.5 kN vs 32.5/19.3 kN) — boundary dimensions match, not a load-rating equivalent. |
| 7306-BEP | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 30×72×19 mm envelope, but catalogue C/C0 differ between executions (53/41.5 kN vs 32.5/19.3 kN) — boundary dimensions match, not a load-rating equivalent. |
| 7306-BECBP | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 30×72×19 mm envelope, but catalogue C/C0 differ between executions (53/41.5 kN vs 35.5/21.2 kN) — boundary dimensions match, not a load-rating equivalent. |
| 7306-BEGAPH | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 30×72×19 mm envelope, but catalogue C/C0 differ between executions (53/41.5 kN vs 35.5/21.2 kN) — boundary dimensions match, not a load-rating equivalent. |
| 7306-BECBM | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 30×72×19 mm envelope, but catalogue C/C0 differ between executions (53/41.5 kN vs 35.5/21.2 kN) — boundary dimensions match, not a load-rating equivalent. |
| 7306-BECBY | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 30×72×19 mm envelope, but catalogue C/C0 differ between executions (53/41.5 kN vs 37.5/23.2 kN) — boundary dimensions match, not a load-rating equivalent. |
| 7306-ACCBM | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 30×72×19 mm envelope, but catalogue C/C0 differ between executions (53/41.5 kN vs 39/23.6 kN) — boundary dimensions match, not a load-rating equivalent. |
| QJ-306-MA | SKF | full Dimensions and internal design equivalent — standard interchange. | Same 30×72×19 mm envelope with catalogue ratings within 10 %; QJ 306 MA is the brass cage, open arrangement, four-point split-inner-ring execution of this size — boundary dimensions interchangeable, execution differs. |
| QJ-306-N2PHAS | SKF | full Dimensions and internal design equivalent — standard interchange. | Same 30×72×19 mm envelope with catalogue ratings within 10 %; QJ 306 N2PHAS is the PEEK cage, open arrangement, four-point split-inner-ring execution of this size — boundary dimensions interchangeable, execution differs. |
| 7306 | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | SKF SKF 7306 BEP shares the 30×72×19 mm angular-contact envelope, but catalogue C/C0 differ (53/41.5 kN vs 32.5/19.3 kN) — envelope match, not a load-rating equivalent. |
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 QJ-306-N2MA model number is decoded
QJ 306 N2MA is SKF's 30 mm-bore QJ four-point contact ball bearing of the QJ300 series, 30×72×19 mm, with a two-piece inner ring for bidirectional axial location beside a radial bearing. QJ identifies a four-point contact ball bearing with a two-piece inner ring: the gothic-arch raceways seat each ball at four points, giving axial location in both directions while a paired radial bearing carries the radial load. N2 marks two locating slots, 180° apart, in one outer-ring side face: pins or dogs engage the slots to stop the outer ring turning in its radially-clear housing bore. machined brass cage, outer-ring-centred (suffix MA), which guides on the outer ring rather than on the balls. Envelope 30×72×19 mm (1.181×2.835×0.748 in), 21.0 mm radial section height, C 53 kN, C0 41.5 kN, Pu 1.76 kN.SKF publishes only the 17,000 r/min limiting speed for this execution, catalogue mass 420 g. At the printed limiting speed of 17,000 r/min the mean pitch diameter dm ≈ 51.0 mm implies a dn value around 867k mm·r/min; only the limiting speed is published for this execution. Speed planning distinguishes the two published ceilings mechanically: the cage and balls tolerate 17,000 r/min and no separate thermal reference is published; at dm ≈ 51.0 mm the corresponding dn is approximately 867k mm·r/min. Speed-ratio note for this exact unit: no thermal reference speed is listed (seal/grease life governs), so the 17,000 r/min limiting value is the single published ceiling. Locating-slot execution: the two N2 notches are milled into one outer-ring side face exactly 180 degrees apart and engaged by housing dogs or headed pins during assembly; verify dog engagement by hand before the cover goes on, deburr the slot edges after any housing rework, and re-inspect the slot roots for fretting marks at each overhaul because a dog that rides only one slot lets the outer ring walk. The slots identify this order number unmistakably: the plain MA/PHAS execution of the same bore has no notches and must be secured differently.
Typical equipment & failure modes
Common applications
- textile machinery traverse drives
- gearbox shafts where one QJ locates axially in both directions beside a radial bearing
- screw and worm drives
Known failure patterns
- axial over-travel when the outer ring is clamped instead of left with radial clearance and a small end-play gap
- two-piece inner-ring separation damage if the split ring is pressed or heated unevenly during mounting
- locating-slot root fretting or dog wear when only one N2 notch carries the anti-rotation torque
- edge loading from shaft deflection or housing misalignment
- edge loading from shaft deflection or housing misalignment
Selection pitfalls — read before you substitute
- Provide a minimum axial load (spring preload is common) so the balls stay correctly seated at speed and light-load conditions; otherwise they skid.
- The MA machined brass cage is outer-ring-centred — inspect its guide clearance when servicing
- The inner ring is two-piece: handle both halves together, mount square, and do not separate the split ring unless the fitting procedure requires it.
- Anti-rotation is built into QJ-306-N2MA: check the two N2 slot faces and the engaging housing dogs at every refit, and never rely on cover friction to stop the radially loose outer ring.
- The MA brass cage of QJ-306-N2MA is outer-ring-centred: its guide land needs an uninterrupted oil film, so check lubricant reach when the bearing is used purely as a thrust location.
- Catalogue ratings are SKF PUB BU/P1 17000 figures for QJ 306 N2MA as the qj slotted execution; the other order numbers of the QJ 306 size are different products and may carry different ratings — always quote the full designation when purchasing.
Frequently asked questions
What are the dimensions and catalogue data of QJ-306-N2MA?
QJ 306 N2MA measures 30 mm bore × 72 mm OD × 19 mm width (1.181 × 2.835 × 0.748 in), mass about 420 g. SKF 17000 ratings: C 53 kN, C0 41.5 kN, Pu 1.76 kN, SKF publishes only the 17,000 r/min limiting speed for this execution.
What does the N2MA suffix mean?
QJ identifies a four-point contact ball bearing with a two-piece inner ring: the gothic-arch raceways seat each ball at four points, giving axial location in both directions while a paired radial bearing carries the radial load. N2 marks two locating slots, 180° apart, in one outer-ring side face: pins or dogs engage the slots to stop the outer ring turning in its radially-clear housing bore. machined brass cage, outer-ring-centred (suffix MA), which guides on the outer ring rather than on the balls.
What minimum axial load does QJ-306-N2MA require?
Like angular-contact bearings the QJ needs a minimum axial load to keep the balls seated — spring preload against the outer ring is typical — and the load ratio Fa/Fr ≥ 1,27 keeps contact on one inner-ring raceway and the opposite outer-ring side.
How is a QJ four-point bearing mounted?
As a thrust/locating bearing with radial clearance in the housing, paired with a separate radial bearing (commonly a cylindrical roller bearing): the QJ locates the shaft axially in both directions, the radial bearing carries radial load. Keep the outer ring unclamped with a small end-play gap; N2 slot executions use dogs to stop the outer ring turning.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018) on 2026-09-27. Read our editorial & correction policy.