QJ-306-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-306-MA model number is decoded

QJ 306 MA is SKF's 30 mm-bore QJ four-point contact ball bearing of the QJ300 series, 30×72×19 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 30×72×19 mm (1.181×2.835×0.748 in), 21.0 mm radial section height, C 53 kN, C0 41.5 kN, Pu 1.76 kN.SKF publishes only the 17,000 r/min limiting speed for this execution, catalogue mass 420 g. Mass and section check: 420 g inside the 30×72×19 mm outline leaves a 21.0 mm radial section, and the 41.5 kN static rating is 0.78× the dynamic rating — plan static safety and minimum load against those numbers rather than against sister executions. Load balance: C0 41.5 kN against C 53 kN gives a 0.78 ratio, typical of a four-point thrust-oriented design; Pu 1.76 kN enters the SKF adjusted-life equation rather than the basic rating life. Bore-to-OD planning: OD 72 over bore 30 is a 2.40× step for this size, and the 19 mm width gives a bore/width ratio of 1.58; use these ratios when housing space around the 30 mm shaft is the first constraint. 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

• Provide a minimum axial load (spring preload is common) so the balls stay correctly seated at speed and light-load conditions; otherwise they skid.
• 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.
• Anti-rotation is NOT built into QJ-306-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-306-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 306 MA as the qj plain execution; the other order numbers of the QJ 306 size are different products and may carry different ratings — always quote the full designation when purchasing.