Fafnir2MM9124WICRQULSuper-Precision Angular Contact Ball Bearing Quad Set 120x180x28 mm, 15 Degree Contact Angle, Light Preload, Phenolic Cage, 4 Pcs

Product Description

What this part is

A set of four Fafnir 2MM9124WI-QUL super-precision angular contact ball bearings, 120 mm bore by 180 mm outside diameter by 28 mm wide, with phenolic cages, ground as a quad stack at light preload. Fafnir is Timken’s super-precision line.

Decoding the designation

The 2MM prefix sets a 15° contact angle and carries P4S precision, equivalent to ABEC 7/9. The leading 9 in 9124 places the bearing in the ISO 70 light dimension series, giving an ISO base number of 7024, and the 24 size code gives a 120 mm bore. WI marks the super-precision angular contact family, CR the phenolic outer-land-riding cage, and QUL a quad set at light preload.

What these specs mean in practice

Four rows in one bearing position give roughly twice the thrust and radial capacity of a duplex pair in the same bore, at the cost of axial length and heat. A 15° contact angle keeps the speed capability up where a 25° would trade it for thrust. Light preload is what makes four rows thermally workable, since preload-generated friction compounds with every row added.

Quantity and configuration

Four bearings, ground as a matched quad set, open with no seals or snap rings.

Fitting notes

The four are installed together in the ground order and orientation, since the offsets are matched across the whole stack. Mounting is onto a clean straight journal against a square shoulder, and the stack is clamped without shims. Phenolic cages absorb lubricant, so the set is run in gently after an oil change.

Interchange guidance

The ISO base number is 7024, so the envelope matches a 7024-series angular contact bearing from any maker. A quad-ground set interchanges only with another quad set at the same angle and preload; duplex pairs and single universal bearings in the same envelope are related sizes.