Fafnir3MM9124WISUMSuper-Precision Angular Contact Ball Bearing – 120 mm Bore, 180 mm OD, 28 mm Width, 25° Contact Angle, Open, Phenolic Machined Cage, Medium Preload, Universally Ground

Product Description

What this part is

Fafnir 3MM9124WI-SUM super-precision angular contact ball bearing, single row, open, universally ground. Bore: 120 mm (4.724 in). Outside Diameter: 180 mm (7.087 in). Bearing Width: 28 mm (1.102 in). Total Width: 28 mm. Series: Fafnir 9100WI spindle series, ISO 7024 envelope. Timken World Part Number: 7024E-T-P4S-SUM. Rolling Elements: steel balls. Bearing Material: through-hardened bearing steel. Cage Type: CR — Phenolic Outer Land Riding Cage. Cage Material: phenolic textile laminate. Closure Type: open. Number of Rows: 1.

Decoding the designation

Contact Angle: 25°. Precision Rating: ISO P4S (ABEC 7/9). Preload: Medium. 3MM is the Fafnir super-precision prefix at the 25° angle, and the MM prefix carries the P4S build. 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 with a low shoulder on both rings. CR is the phenolic cage riding on the outer ring land. SUM is single, universally ground, medium preload. Searchable forms of the number include 3MM9124WI-SUM, 3MM9124WISUM, 3MM9124WICRSUM, 3MM-9124-WI-CR-SUM, 3MM 9124 WI CR SUM and 7024-A.

What these specs mean in practice

Dynamic Load Rating (C1, Timken 1M revs): 105 kN / 23,600 lbf. Dynamic Load Rating (C1 ISO, per row): 95.6 kN / 21,500 lbf. Static Load Rating (C0): 103.2 kN / 23,200 lbf. Limiting Speed, grease: 6,900 rpm. Limiting Speed, oil: 12,400 rpm. A 25° contact angle carries substantially more thrust than a 15° bearing of the same envelope and gives a stiffer axial response; against a 30° or 40° bearing it runs faster and generates less heat. Medium preload sits between the light setting used for maximum speed and the heavy setting used for maximum stiffness. 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). Bore Type: straight.

Quantity and configuration

One bearing. Unit Quantity: 1 Pc. Rows per set: single. Item Weight: 4.81 lbs. 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 for a narrower effective spread, or a tandem set to double one-direction thrust, each developing the specified medium preload when clamped solid.

Interchange guidance

Same-envelope 25° super-precision equivalents at medium preload 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° 2MM9124WI shares the envelope at a different contact angle and is a related size.