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 (1.9685 in). Outside Diameter: 72 mm (2.8346 in). Overall Width: 12 mm (0.4724 in) per bearing. Total Width: 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

Contact Angle: 25°. Precision Class: P4S (ABEC 7/9). Series: Fafnir Ultra-Light 9300WI, which maps to the ISO 719 dimension family and gives the 71910 envelope of 50 x 72 x 12 mm. Cage Material: Phenolic (fabric-base laminate). Cage Type: Machined, outer-land riding, from the CR carton marking. Arrangement: DUM, a universal duplex pairing. Preload: Medium. Searchable forms of the number: 3MM9310WI-DUM, 3MM9310WIDUM, 3MM 9310 WI CR DUM, 3MM-9310-WI-DUM, 3MM9310WI.

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. 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.

Mounting data

Item Weight: 0.30 lb (0.136 kg) per bearing. Maximum shaft or housing fillet radius cleared by the bearing corner: 0.6 mm (0.024 in). Bore Type: Straight, on an interference-fit shaft seat, with the outer rings located in a bored housing.

Materials and construction

Bearing Material: chrome bearing steel. Rolling Elements: steel balls. Number of Rows: 1 per bearing, 2 rows in the mounted set. Closure Type: Open, both faces. Internal Clearance: N/A — the DUM execution is preload-set. Lubricant: oil or oil-air.

Quantity and configuration

Unit Quantity: 2 Pcs, one matched universal duplex set. The rings are ground as a matched unit at the factory, so the pair can be arranged back-to-back, face-to-face or in tandem, developing medium preload from the ground ring offset in any of those arrangements.

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. Carton cross-references: 71910 E T DUM P4, 7910ACD and 7910A5. 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.

Applications

Machine tool spindles, grinding spindles, instrument drives and precision gearboxes where radial space is tight. Harmonization Code: 8482.10.50.28.