QJ-308-N2MA bearing: complete specifications & equivalents

Specification table

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.

Cross references & equivalents

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-308-N2MA model number is decoded

QJ 308 N2MA is SKF's 40 mm-bore QJ four-point contact ball bearing of the QJ300 series, 40×90×23 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 40×90×23 mm (1.575×3.543×0.906 in), 25.0 mm radial section height, C 78 kN, C0 64 kN, Pu 2.7 kN.SKF publishes only the 14,000 r/min limiting speed for this execution, catalogue mass 780 g. Envelope economics: the 23 mm width over a 25.0 mm section yields 0.92 mm of ring width per section millimetre, and the bearing weighs 780 g for 78 kN of dynamic capacity — about 10 g per rated kN. Selection figures for QJ 308 N2MA: the static-to-dynamic ratio C0/C is 0.82, Pu 2.7 kN is about 3 % of C, and catalogue mass works out to roughly 20 g per millimetre of bore. Bore-to-OD planning: OD 90 over bore 40 is a 2.25× step for this size, and the 23 mm width gives a bore/width ratio of 1.74; use these ratios when housing space around the 40 mm shaft is the first constraint. 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

Selection pitfalls — read before you substitute

• Run the QJ as a thrust bearing with radial clearance in the housing, paired with a separate radial bearing; the QJ outer ring must not be radially clamped.
• Apply the Fa/Fr ≥ 1,27 condition: at lower ratios the balls contact both sides of a raceway, increasing friction and shortening life — the paired radial bearing should carry the radial share.
• Engage the N2 slots with housing dogs at assembly — a radially loose outer ring without positive anti-rotation creeps its seat
• Anti-rotation is built into QJ-308-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-308-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 308 N2MA as the qj slotted execution; the other order numbers of the QJ 308 size are different products and may carry different ratings — always quote the full designation when purchasing.