BA-3 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-3 model number is decoded

BA 3 is SKF's BA-series miniature single-direction thrust ball bearing for a 3 mm shaft — the BA digits give bore in millimetres directly — supplied as a shaft washer, a housing washer and a stamped sheet-steel ball-cage assembly, 3×8×3.5 mm. The separable set comprises a shaft washer (ground bore, tight fit on the shaft), a loose-bore housing washer and one ball-cage assembly, reacting axial force in one direction and carrying no radial load. the BA prefix marks SKF miniature thrust ball bearings for shaft diameters below 10 mm — the digits give the bore in millimetres directly, so a BA 3 fits a 3 mm shaft rather than using the two-digit bore code. BA miniatures use the standard stamped sheet-steel ball-cage assembly: two pressed steel washers retain a small ball complement, and at these dimensions the cage and washers are handled as three loose parts. Envelope 3×8×3.5 mm (0.118×0.315×0.138 in), 2.5 mm radial section, C 0.806 kN, C0 0.72 kN, Pu 0.027 kN. reference speed 26,000 r/min (thermal) and limiting speed 36,000 r/min (mechanical), catalogue mass 1 g. Load balance: C0 0.72 kN against C 0.806 kN gives a 0.89 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. Bore-to-OD planning: OD 8 over bore 3 is a 2.67× step for this size, and the 3.5 mm height gives a bore/height ratio of 0.86; use these ratios when the housing recess around the 3 mm shaft is the first constraint. Sizing arithmetic on the 3 mm bore: 0.806 kN C over the 2.5 mm radial section gives 0.3 kN per section millimetre, and the 3.5 mm stack height is 1.40× that section — proportions typical of a BA thrust section. Mass and section check: 1 g inside the 3×8×3.5 mm outline leaves a 2.5 mm radial section, and the 0.72 kN static rating is 0.89× the dynamic rating — plan static safety and minimum preload against those figures. Envelope economics: the 3.5 mm axial height over a 2.5 mm radial section yields 0.2 kN of dynamic capacity per height millimetre, and the bearing weighs 1 g for 0.806 kN C — about 1 g per rated kN. 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 3 mm bore: never grease-pack a BA bearing — one tiny dot of instrument oil on the ball set is enough, since the 1 g assembly will hydroplane its own cage out of position inside a flooded 8 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 3 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.
• Identify the washers before fitting: the shaft washer has the ground, smaller bore and takes an interference fit on the 3 mm shaft, while the housing washer bore is larger and runs loose; swapping them locks the ball set and burns the tracks.
• The three components are separable and interchangeable within the ISO 104 size, but keep this bearing's parts together in service and never combine washers from different manufacturers or a worn washer with a new ball set.
• The BA 3 is a pure axial bearing: it must never be subjected to radial load — any radial force on the 3 mm shaft has to be carried by a radial bearing mounted alongside it.
• There is no 51xxx coded size below 10 mm bore: the BA range is the miniature entry point for pure axial location, and at 3 mm the limit loads are small enough that shaft and housing squareness, not capacity, usually governs the design.
• Ordering discipline for BA 3: the catalogue page quotes BA 3 and its 0.806/0.72 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.