Fafnir3MM9124WI-SUMSuper Precision Angular Contact Ball Bearing 120 x 180 x 28 mm, 25° Contact Angle, P4S / ABEC 7 Class, Phenolic Cage, Single Universal Medium Preload

Product Description

What this part is

Fafnir 3MM9124WI-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: 7024E-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

3MM is the Fafnir super-precision prefix. Contact Angle: 25°. 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 3MM9124WI-SUM, 3MM9124WISUM, 3MM9124WICRSUM, 3MM 9124 WI CR SUM and 3MM9124WIDUM.

What these specs mean in practice

Dynamic Radial Load Rating (C1, Timken 1M revs): 105 kN / 23,600 lbf. Dynamic Radial Load Rating (C1 ISO, per row): 95.6 kN / 21,500 lbf. Static Radial Load Rating (C0): 103.2 kN / 23,200 lbf. Limiting Speed, grease: 6,900 rpm. Limiting Speed, oil: 12,400 rpm. The 70xx series is the thin-section spindle family, a comparatively slim ring for a 120 mm bore, which keeps mass and outside diameter down and lets the bearing run faster than a heavier 72xx section. A 25° contact angle sits in the middle of the spindle range: against a 15° bearing it takes substantially more thrust and gives a stiffer axial response, and against a 30° or 40° bearing it runs faster and generates less heat. Medium preload follows the same logic, giving more rigidity under cutting load than light preload for more heat generated at 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 25° equivalents include NSK 7024A5, FAG B7024-E-T-P4S-UM, SKF 7024 ACD/P4A, RHP 7024-E-T-SUM-P4 and NTN 7024 in the corresponding precision grade. Timken’s own world part number for this bearing is 7024E-T-P4S-SUM, and E denotes the 25° angle in that scheme. The 15° sibling is 2MM9124WI, the same dimensions at a different contact angle and a related size rather than a substitution.