Fafnir3MM209WIDUMSuper-Precision Angular Contact Ball Bearing – 45 mm ID, 85 mm OD, 19 mm Width, Straight Bore, Open, 25 Degree, Medium Preload Universal Duplex Set of 2

Product Description

What this part is

Fafnir 3MM209WI-DUM super-precision angular contact ball bearing, supplied as a universally ground duplex set of two. Bore 45 mm, outside diameter 85 mm, width 19 mm per bearing, 38 mm across the mounted pair. Open on both faces, high carbon chrome steel rings and balls with a machined phenolic cage. The ISO equivalent is a 7209 at 25°.

Decoding the designation

The 3MM prefix marks a 25° contact angle, and the MM prefix carries the P4S precision class, ABEC 7/9. 209 places the bearing in the 200WI series, which maps to the ISO 72 medium dimension family, giving a 7209 envelope of 45 x 85 x 19 mm. WI is the series designation. DUM is a universal duplex pairing at medium preload.

What these specs mean in practice

A 25° contact angle carries substantially more thrust than a 15° bearing in the same envelope, at the cost of some speed capability, which makes it the choice for a spindle or screw drive that sees real axial load. Dynamic load rating 38.4 kN, static load rating 28.5 kN. The 72 medium series gives a thicker ring section than the 70 light series, so it is stiffer under load in the same bore. The machined phenolic cage is light and self-lubricating and suits oil, oil-air or light grease.

Quantity and configuration

Two bearings, universally ground so the pair can be arranged back-to-back, face-to-face or in tandem, developing medium preload in any of those arrangements. Being preloaded, the set carries no radial internal clearance value.

Fitting notes

Straight bore on an interference fit shaft seat, outer rings located in a bored housing. The pair is ground as a matched unit at the factory and stays together. Preload comes from the ground ring offset, so no shim stack or spacer is required.

Interchange guidance

The same-specification equivalent at 25° and P4 in this envelope is the SKF 7209 ACD/P4A DGB, with the FAG B7209-E-T-P4S-DUM and NSK 7209A5TYNDUMP4 alongside it. A 2MM209WI-DUM shares the 45 x 85 x 19 mm envelope at 15°, making it a related size rather than an interchange, and a 3MM209WI-DUL is the same set at light preload.