QJ-309-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-309-MA model number is decoded

QJ 309 MA is SKF's 45 mm-bore QJ four-point contact ball bearing of the QJ300 series, 45×100×25 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 45×100×25 mm (1.772×3.937×0.984 in), 27.5 mm radial section height, C 100 kN, C0 83 kN, Pu 3.55 kN.SKF publishes only the 12,000 r/min limiting speed for this execution, catalogue mass 1050 g. Speed planning distinguishes the two published ceilings mechanically: the cage and balls tolerate 12,000 r/min and no separate thermal reference is published; at dm ≈ 72.5 mm the corresponding dn is approximately 870k mm·r/min. Sizing arithmetic on the 45 mm bore: 100 kN C divided by the 27.5 mm radial section height gives 3.6 kN per section millimetre; the 1050 g mass and 4 % 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 12,000 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.
• 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 NOT built into QJ-309-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-309-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 309 MA as the qj plain execution; the other order numbers of the QJ 309 size are different products and may carry different ratings — always quote the full designation when purchasing.