Fafnir3MM9109WIDUMSuper-Precision Angular Contact Ball Bearing – 45 mm ID, 75 mm OD, 16 mm Width, 25° Contact Angle, Phenolic Cage, Medium Preload, Matched Pair

Product Description

What this part is

A Timken Fafnir 3MM9109WI-CR-DUM super-precision angular contact ball bearing, supplied as a matched pair. Bore 45 mm, outside diameter 75 mm, width 16 mm per bearing, 32 mm across the assembled pair. Open on both faces, with a fabric-base phenolic cage riding on the outer ring lands.

Decoding the designation

The leading 3MM sets a 25° contact angle. The MM prefix denotes Fafnir super-precision execution to P4S, equivalent to ABEC 7/9. The 9100 series number decodes to the ISO 70 light series, so 9109 is the ISO 7009 envelope at 45 x 75 x 16 mm. CR is the phenolic outer-land-riding cage. DUM is a universally matchable duplex pair set to medium preload.

What these specs mean in practice

A 25° contact angle carries more thrust and tolerates less speed than a 15° bearing of the same envelope, which suits it to machine tool spindles and screw drives where axial stiffness governs. The phenolic cage is light and self-lubricating, allowing higher speed than a machined bronze cage while accepting a lower maximum temperature. Because the pair is preload-set rather than clearance-set, internal clearance is not applicable to it.

Quantity and configuration

Two bearings, sold as a matched set. Universally matchable duplex construction allows the pair to be mounted back-to-back, face-to-face or in tandem, with the flush ground faces producing the specified medium preload when clamped.

Fitting notes

The rings are ground for a specific relationship to one another and are kept together as a set. Clamping is applied evenly against the ground faces so that the designed preload is established without distorting the rings.

Interchange guidance

Same-specification equivalents in other schemes are SKF 7009 ACD/P4A DGB, NSK 7009A5TYNDUMP4 and FAG B7009-E-T-P4S-DUM. A 7009 CD, C or 15° variant shares the envelope but carries a different contact angle and is a related size rather than an interchange.