BA-9 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-9 model number is decoded

BA 9 is SKF's BA-series miniature single-direction thrust ball bearing for a 9 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, 9×20×7 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 9 fits a 9 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 9×20×7 mm (0.354×0.787×0.276 in), 5.5 mm radial section, C 3.12 kN, C0 3.8 kN, Pu 0.143 kN. reference speed 12,000 r/min (thermal) and limiting speed 16,000 r/min (mechanical), catalogue mass 10 g. Capacity density: 3.12 kN C from 0.010 kg of bearing steel gives about 312.0 kN per kilogram; static density is correspondingly 380.0 kN/kg at C0 3.8 kN. Section proportions: the 5.5 mm radial section compares with 9 mm of bore (section/bore ≈ 0.61) and the 7 mm height is 1.27× that section — the proportions that identify the BA envelope at a glance. Speed band width for this size is 4,000 r/min between reference and limiting (1.33× ratio); lubrication, preload and heat removal decide where inside that band BA 9 can actually run. Sizing arithmetic on the 9 mm bore: 3.12 kN C over the 5.5 mm radial section gives 0.6 kN per section millimetre, and the 7 mm stack height is 1.27× that section — proportions typical of a BA thrust section. At the printed limiting speed of 16,000 r/min the mean pitch diameter dm ≈ 14.5 mm implies a dn value around 232k mm·r/min; the 12,000 r/min reference speed is the thermal-planning value under catalogue load. 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 9 mm bore: never grease-pack a BA bearing — one tiny dot of instrument oil on the ball set is enough, since the 10 g assembly will hydroplane its own cage out of position inside a flooded 20 mm OD recess.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• 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.
• Keep the applied thrust above Fam ≈ A·(n·dm/1000)² with the printed factor A 7.50×10^-5; for BA 9 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 9 mm shaft, while the housing washer bore is larger and runs loose; swapping them locks the ball set and burns the tracks.
• The third digit grades the section: 511 light, then 512, 513 and 514 progressively taller and heavier at the same bore — select from 3.12/3.8 kN and the available 20 mm OD, never substitute a lighter series for a heavier one without rechecking C and C0.
• There is no 51xxx coded size below 10 mm bore: the BA range is the miniature entry point for pure axial location, and at 9 mm the limit loads are small enough that shaft and housing squareness, not capacity, usually governs the design.
• The 3.12/3.8 kN figures belong to BA 9 specifically (the miniature ba execution of BA 9); suffixed, sphered and counterpart-series order numbers are separate articles, so write the complete designation on the order and the maintenance record.