Fafnir2MM9124WI-SUMSuper Precision Angular Contact Ball Bearing 120 x 180 x 28 mm, 15° Contact Angle, P4S / ABEC 7 Class, Phenolic Cage, Single Universal Medium Preload

Product Description

What this part is

Fafnir 2MM9124WI-SUM super-precision angular contact ball bearing, single row, open, universally ground. Bore: 120 mm. Outside Diameter: 180 mm. Bearing Width: 28 mm. Total Width: 28 mm. Series: Fafnir 9100WI spindle series, ISO 7024 envelope. Timken World Part Number: 7024C-T-P4S-SUM. Rolling Elements: steel balls. Cage Type: CR – Phenolic Outer Land Riding Cage. Cage Material: phenolic textile laminate. Closure Type: open.

Decoding the designation

2MM is the Fafnir super-precision prefix. Contact Angle: 15°. Precision Rating: ISO P4S (ABEC 7/9). The Fafnir 91xx block maps to the ISO 70xx dimension series, so 9124 is the 7024 envelope at 120 x 180 x 28 mm. WI identifies the super-precision angular contact spindle family. CR is the phenolic cage riding on the outer ring land. SUM is single, universally ground, medium preload. Preload: Medium. Searchable forms of the number include 2MM9124WI-SUM, 2MM9124WISUM, 2MM9124WICRSUM, 2MM 9124 WI CR SUM and 2MM9124WIDUM.

What these specs mean in practice

Dynamic Radial Load Rating (C1, Timken 1M revs): 111.2 kN / 25,000 lbf. Dynamic Radial Load Rating (C1 ISO, per row): 101 kN / 22,700 lbf. Static Radial Load Rating (C0): 108.5 kN / 24,400 lbf. Limiting Speed, grease: 6,900 rpm. Limiting Speed, oil: 13,800 rpm. The 15° contact angle is the speed-biased choice: a shallow angle keeps the ball from climbing the raceway shoulder, which cuts ball spin, friction and heat, so the bearing runs faster and cooler than the 25° version of the same envelope. The trade is thrust capacity and axial stiffness. Medium preload partly offsets that, giving more rigidity than light preload for some heat generation and speed. The phenolic outer-land-riding cage, at roughly a fifth the density of brass, loads itself far less under centrifugal force, and the laminate holds a small oil reserve; outer-land riding keeps the cage guided by the outer ring so it stays concentric at speed.

Mounting dimensions

Shaft Backing Shoulder Diameter: 132.5 mm (5.220 in). Housing Backing Shoulder Diameter: 168.3 mm (6.630 in). Maximum Shaft Fillet Radius: 2 mm (0.079 in). Outer Ring To Clear Radius: 2 mm (0.079 in).

Quantity and configuration

One bearing. Unit Quantity: 1 Pc. Rows per set: single. The SUM suffix denotes a single universally ground bearing, and universal grinding is what makes a single useful: two or more of these clamp together into a back-to-back set for maximum moment stiffness and two-direction thrust, a face-to-face set where housing alignment is imperfect, or a tandem set to double one-direction thrust, each developing the specified medium preload when clamped solid.

Interchange guidance

Fafnir super precision is supplied under the Timken brand and the Fafnir numbers remain in active cross-reference use. Same-envelope 15° equivalents include NSK 7024C, FAG B7024-C-T-P4S-UM, SKF 7024 CD/P4A, RHP 7024-C-T-SUM-P4 and NTN 7024C in the corresponding precision grade. The 7024-C designation carried on this listing is consistent: C denotes 15° in FAG and NSK nomenclature, matching the Fafnir 2MM prefix, and Timken’s own world part number is 7024C-T-P4S-SUM. The 25° sibling is 3MM9124WI, the same dimensions at a different contact angle and a related size rather than a substitution.