Fafnir2MM9304WICRDULAngular Contact Ball Bearing — 20 mm ID, 37 mm OD, 9 mm Width, 15° Contact Angle, Light Preload, Phenolic Cage, ABEC 7/9

Product Description

What this part is

Fafnir 2MM9304WICRDUL, a super-precision spindle angular contact ball bearing from Timken’s Fafnir 9300WI range. Bore: 20 mm. Outside Diameter: 37 mm. Bearing Width: 9 mm per bearing. Total Width: 18 mm across the set. Contact Angle: 15°. Precision Class: ABEC 7/9 (P4S). Preload: light. Cage Type: CR, phenolic outer land riding. Cage Material: phenolic. Rolling Elements: steel balls. Number of Rows: 1 per bearing. Manufacturer Part Number: 2MM9304WI DUL. World Part Number: 71904C-T-P4S-DUL.

Decoding the designation

2MM — Fafnir super-precision spindle execution at a 15° contact angle, ground to ABEC 7/9 (P4S) tolerance.

9304 — 9300WI dimension series, bore code 04. That is the ISO 71904 envelope: 20 mm bore, 37 mm outside diameter, 9 mm width per bearing.

WI — low shoulder on both rings, which is what allows the high ball complement and the 15° angle to be ground into this section.

CR — phenolic outer land riding cage, guided on the outer ring lands.

DUL — duplex, light preload. Two universally ground bearings supplied as a matched set, so the faces are flush-ground and any two of them close to the same preload when clamped.

What these specs mean in practice

Dynamic Radial Load Rating (C1): 8,080 N (1,820 lbf) per bearing. Dynamic Radial Load Rating, ISO method (C1 per row): 7,340 N (1,660 lbf). Static Radial Load Rating (C0): 4,560 N (1,020 lbf) per bearing. Limiting Speed, grease: 42,100 rpm. Limiting Speed, oil: 84,200 rpm.

The 15° contact angle puts the load path close to radial, which is what buys the speed: 42,100 rpm on grease in a 20 mm bore is machine-tool spindle territory. A 25° build on the same envelope trades that speed away for thrust capacity. The phenolic outer land riding cage is light, runs quiet and holds oil in its own porosity, which is why it is the standard cage on spindle duty. Light preload sets the stiffness without loading the balls hard enough to drive the running temperature up.

Quantity and configuration

Unit Quantity: 2 Pcs. A matched duplex set of two universally ground bearings, 18 mm total width when clamped together.

Mounting data

Shaft Backing Shoulder Diameter: 23.9 mm (0.940 in). Housing Backing Shoulder Diameter: 33.7 mm (1.330 in). Maximum Shaft Fillet Radius: 0.3 mm (0.012 in). Outer Ring To-Clear Radius: 0.3 mm (0.012 in).

Interchange guidance

Timken’s world part number for this bearing is 71904C-T-P4S-DUL. Searchable variants of the Fafnir number: 2MM9304WI-DUL, 2MM9304WICRDUL, 2MM-9304-WI-CR-DUL, 2MM 9304 WI CR DUL, 7904C.

The 3MM9304WI on the same 20 x 37 x 9 mm envelope is the 25° build: more thrust capacity, lower speed.