QJ-308-MA 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-MA model number is decoded

QJ 308 MA 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. 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. The 2.7 kN fatigue load limit is the equivalent-load floor for long-life adjustment; with 78/64 kN ratings and 780 g mass this execution carries about 1.95 kN of C per millimetre of bore. Sizing arithmetic on the 40 mm bore: 78 kN C divided by the 25.0 mm radial section height gives 3.1 kN per section millimetre; the 780 g mass and 3 % Pu/C share frame the light-load floor for the adjusted-life check. Speed-ratio note for this exact unit: no thermal reference speed is listed (seal/grease life governs), so the 14,000 r/min limiting value is the single published ceiling. Plain outer-ring execution: this order number is delivered without N2 locating slots, so anti-rotation is solved in the housing instead — a shoulder dog, a spring-loaded key, a cover feature or an interference-free circlip arrangement. Because the outer ring deliberately runs with radial clearance and a small axial float gap, omitting positive anti-rotation invites seat fretting; the slotted N2 order number is the alternative when the housing can provide engagement pins.

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.
• Without N2 slots, provide another positive anti-rotation feature for the radially loose outer ring
• Keep a small axial gap between the outer ring and the cover flange so it can accommodate thermal movement; never clamp the outer ring solid.
• Anti-rotation is NOT built into QJ-308-MA: without N2 slots the housing must provide a dog, keyed cover or other positive stop, since the outer ring runs radially loose by design.
• The MA brass cage of QJ-308-MA 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 MA as the qj plain 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.