QJ-304-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-304-MA model number is decoded

QJ 304 MA is SKF's 20 mm-bore QJ four-point contact ball bearing of the QJ300 series, 20×52×15 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 20×52×15 mm (0.787×2.047×0.591 in), 16.0 mm radial section height, C 32 kN, C0 21.6 kN, Pu 0.93 kN.SKF publishes only the 24,000 r/min limiting speed for this execution, catalogue mass 180 g. Sizing arithmetic on the 20 mm bore: 32 kN C divided by the 16.0 mm radial section height gives 2.0 kN per section millimetre; the 180 g mass and 3 % Pu/C share frame the light-load floor for the adjusted-life check. The 0.93 kN fatigue load limit is the equivalent-load floor for long-life adjustment; with 32/21.6 kN ratings and 180 g mass this execution carries about 1.60 kN of C per millimetre of bore. Speed-ratio note for this exact unit: no thermal reference speed is listed (seal/grease life governs), so the 24,000 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

• 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.
• 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 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 NOT built into QJ-304-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-304-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 304 MA as the qj plain execution; the other order numbers of the QJ 304 size are different products and may carry different ratings — always quote the full designation when purchasing.