BA-4 bearing: complete specifications & equivalents

Specification table

Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018)) · extracted 2026-09-28

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 BA-4 model number is decoded

SKF lists BA 4 in the BA miniature range: a single-direction thrust ball bearing of 4 mm bore (stated directly in the order number), 4×10×4 mm, built from two thin pressed washers and a miniature ball-cage assembly. The bearing is delivered as separate, interchangeable parts: a ground-bore shaft washer, a loose-bore housing washer and the ball-cage assembly between them, designed for one axial load direction only. the BA numbering convention is literal for miniature sizes — BA 4 names a 4 mm shaft outright, bridging the gap where the coded 51xxx range does not yet begin. cage-wise BA bearings follow the standard pressed sheet-steel design: the retainer separates the miniature ball complement and is handled as one of the three loose components. Envelope 4×10×4 mm (0.157×0.394×0.157 in), 3.0 mm radial section, C 0.761 kN, C0 0.72 kN, Pu 0.027 kN. reference speed 22,000 r/min (thermal) and limiting speed 30,000 r/min (mechanical), catalogue mass 2 g. Speed-ratio note for this exact unit: the reference speed is 22,000 r/min against a 30,000 r/min limiting speed, a reference-to-limit ratio of 0.73. Speed band width for this size is 8,000 r/min between reference and limiting (1.36× ratio); lubrication, preload and heat removal decide where inside that band BA 4 can actually run. Pitch-diameter arithmetic: dm = (4+10)/2 = 7.0 mm; at the 30,000 r/min limiting speed that corresponds to roughly 210k mm·r/min, the figure used when comparing cage speed demand across the thrust-ball series. Sizing arithmetic on the 4 mm bore: 0.761 kN C over the 3.0 mm radial section gives 0.3 kN per section millimetre, and the 4 mm stack height is 1.33× that section — proportions typical of a BA thrust section. Load balance: C0 0.72 kN against C 0.761 kN gives a 0.95 ratio — thrust ball bearings are chosen on static rating and F_a/C0 far more often than on L10 life, while Pu 0.027 kN enters the adjusted-life check. Miniature handling note: the three BA components — shaft washer, housing washer and ball-cage assembly — are supplied loose and separate on contact, so mount the unit inside its housing recess before the shaft is offered; a dropped BA set scatters washers and balls that are nearly impossible to sort by eye, and a washer fitted reversed cannot be seen from outside once the cover is on. Service note at 4 mm bore: never grease-pack a BA bearing — one tiny dot of instrument oil on the ball set is enough, since the 2 g assembly will hydroplane its own cage out of position inside a flooded 10 mm OD recess.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• Keep the applied thrust above Fam ≈ A·(n·dm/1000)² with the printed factor A 3.00×10^-6; for BA 4 a spring preload or the rotor weight is part of the selection at light load and high speed, because unloaded balls skid rather than roll.
• The BA 4 is a pure axial bearing: it must never be subjected to radial load — any radial force on the 4 mm shaft has to be carried by a radial bearing mounted alongside it.
• On vertical shafts retain the loose housing washer positively with a cover or ring and verify the grease fill does not drain out of the 4 mm stack; thrust-ball bearings on horizontal shafts should have the shaft washer (the tight one) against the rotating element.
• Identify the washers before fitting: the shaft washer has the ground, smaller bore and takes an interference fit on the 4 mm shaft, while the housing washer bore is larger and runs loose; swapping them locks the ball set and burns the tracks.
• There is no 51xxx coded size below 10 mm bore: the BA range is the miniature entry point for pure axial location, and at 4 mm the limit loads are small enough that shaft and housing squareness, not capacity, usually governs the design.
• Ordering discipline for BA 4: the catalogue page quotes BA 4 and its 0.761/0.72 kN ratings as one exact article; bare-number substitutions from another series or brand need a fresh dimension and rating check, not a like-for-like assumption.