QJ-311-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-311-N2MA model number is decoded

QJ 311 N2MA is SKF's 55 mm-bore QJ four-point contact ball bearing of the QJ300 series, 55×120×29 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 55×120×29 mm (2.165×4.724×1.142 in), 32.5 mm radial section height, C 137 kN, C0 118 kN, Pu 5 kN.SKF publishes only the 10,000 r/min limiting speed for this execution, catalogue mass 1750 g. Speed planning distinguishes the two published ceilings mechanically: the cage and balls tolerate 10,000 r/min and no separate thermal reference is published; at dm ≈ 87.5 mm the corresponding dn is approximately 875k mm·r/min. At the printed limiting speed of 10,000 r/min the mean pitch diameter dm ≈ 87.5 mm implies a dn value around 875k mm·r/min; only the limiting speed is published for this execution. Bore-to-OD planning: OD 120 over bore 55 is a 2.18× step for this size, and the 29 mm width gives a bore/width ratio of 1.90; use these ratios when housing space around the 55 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

• The MA machined brass cage is outer-ring-centred — inspect its guide clearance when servicing
• 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.
• The MA machined brass cage is outer-ring-centred — inspect its guide clearance when servicing
• Anti-rotation is built into QJ-311-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-311-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 311 N2MA as the qj slotted execution; the other order numbers of the QJ 311 size are different products and may carry different ratings — always quote the full designation when purchasing.