Fafnir3MM9310WIDUMSuper-Precision Angular Contact Ball Bearing – 50 mm ID, 72 mm OD, 12 mm Width, Open, 25 Degree, Medium Preload Universal Duplex Set of 2

Product Description

What this part is

Fafnir 3MM9310WI-DUM super-precision angular contact ball bearing, supplied as a universally ground duplex set of two. Bore 50 mm, outside diameter 72 mm, width 12 mm per bearing, 24 mm across the mounted pair. Open on both faces, chrome steel rings and balls with a machined phenolic cage. The ISO equivalent is a 71910 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. 9310 places the bearing in Timken’s ultra-light 9300WI series, which maps to the ISO 719 dimension family, giving a 71910 envelope of 50 x 72 x 12 mm. CR is the phenolic outer-land-riding cage. DUM is a universal duplex pairing at medium preload.

What these specs mean in practice

A 25° contact angle carries more thrust and less speed than a 15° bearing in the same envelope, which makes it the choice where a spindle sees significant axial load. Dynamic load rating 16.6 kN and static load rating 13.8 kN per bearing. The 719 ultra-light section keeps the outside diameter small for the bore, which suits compact spindle noses and instrument drives where radial space is tight. The phenolic cage is light and low friction and prefers oil or oil-air lubrication.

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 rings are ground as a matched unit at the factory and stay together. Preload comes from the ground ring offset, so no shim stack or spacer is required.

Interchange guidance

Same-specification equivalents at 25° in the 71910 envelope are the FAG 71910-E-T-P4S-DUM, SKF 71910 ACD/P4A DGB and NSK 7910A5TYNDUMP4. A 2MM9310WI-DUM shares the 50 x 72 x 12 mm envelope at 15°, making it a related size rather than an interchange, and a 3MM9310WI-DUL is the same set at light preload.