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, 120 mm bore, 180 mm outside diameter, 28 mm width. Single row, open on both faces, machined phenolic outer-land-riding cage. ISO base number 7024.

Decoding the designation

3MM sets a 25° contact angle in the Fafnir WI super-precision scheme, and the MM prefix carries P4S precision — ABEC 7 dimensional tolerances with ABEC 9 running accuracy. The leading 9 of 9124 places the bearing in the ISO 70 light dimension series, so the ISO base number is 7024. WI is the ground spindle-bearing execution, CR the phenolic outer-land-riding cage, SU a single universally ground bearing, and M medium preload.

What these specs mean in practice

A 25° contact angle carries substantially more thrust than a 15° bearing of the same envelope, and gives up speed and some radial stiffness in exchange. Basic dynamic capacity is 87.5 kN (19,670 lbf) and static capacity 93 kN (20,900 lbf), with a limiting speed of 5,300 rpm. Medium preload sits between the light setting used for maximum speed and the heavy setting used for maximum stiffness, and is the usual choice where a spindle has to hold accuracy under cutting thrust.

Quantity and configuration

One bearing. Universally ground, so it stacks with any other bearing of the same designation in a back-to-back, face-to-face or tandem set without a matched-set order code.

Fitting notes

Straight bore on an interference fit to the spindle journal, outer ring clamped square in the housing. Where two or more are stacked the marked faces are oriented per the chosen arrangement, and the medium preload is developed by the ground offsets rather than by shimming. Operating range is –30 to 120 °C on oil or grease.

Interchange guidance

Same-specification 25° super-precision equivalents include the SKF 7024 ACD/P4A, FAG B7024-E-T-P4S, NSK 7024A5TYNSULP4 and RHP 7024ETDUMP4. A 2MM9124WI of the same envelope is a 15° bearing and a related size rather than a substitution, and a DU-suffixed 3MM9124WI is a matched duplex pair rather than a single.