Fafnir3MM9122WIDUHSuper Precision Angular Contact Ball Bearing Duplex Pair – Straight Bore, 110 mm ID, 170 mm OD, 28 mm Width Each, 56 mm Stacked, Open, 25 Degree Contact Angle, Heavy Preload, Phenolic Cage

Product Description

What this part is

A Timken Fafnir 3MM9122WI-CR-DUH super precision angular contact ball bearing set, furnished as a factory-matched duplex pair. Each bearing measures 110 mm bore by 170 mm outside diameter by 28 mm wide, giving 56 mm across the mounted pair. Contact angle is 25°, the cage is phenolic and outer-land riding, and both faces are open. The ISO equivalent number is 7022.

Decoding the designation

In the Fafnir super precision scheme the leading 3MM sets the contact angle at 25°, and the MM prefix itself denotes P4S tolerancing. The leading 9 marks the ISO 70 light dimension series, and 9122 in the 9100WI family corresponds to ISO 7022. WI is universally ground, meaning the ring faces are machined so that bearings from the family stack in any arrangement. CR is the phenolic outer-land-riding cage. DUH resolves as duplex pair, heavy preload, which is why the set ships as two bearings.

What these specs mean in practice

A 25° contact angle carries more thrust and less speed than a 15° bearing of the same envelope, so this pair suits spindles where axial cutting load matters more than top rpm. P4S holds bore and outside diameter to ABEC 7 while running accuracy is held to ABEC 9, which is the combination machine tool builders specify for shaft position repeatability.

Heavy preload removes all internal play and raises the pair’s axial and radial stiffness, so the shaft deflects less under load and the balls are held in a defined contact path from the first revolution. The cost is heat generation and a lower speed ceiling than a light or medium preload of the same designation. A phenolic outer-land-riding cage is light, self-lubricating from resin-impregnated fabric, and rides on the outer ring land where it is stable at speed, which is why it appears on grease-lubricated high-precision spindle bearings.

Quantity and configuration

Two bearings, supplied as one matched DUH duplex set with the preload ground into the ring faces at the factory. Per-bearing dynamic load rating is 114 kN and static rating 112 kN, with a limiting speed of 9500 rpm. Mass is 4.41 lbs for the set.

Fitting notes

The preload is established by the ground offset on the ring faces, so the pair is mounted with the match marks aligned and clamped solid against square shoulders; no shimming or measured clearance setting applies. Shaft and housing seats are ground to the fits published for P4S super precision bearings, since a slack or tight seat transfers directly into the running accuracy the tolerance grade was bought for.

Interchange guidance

The direct SKF equivalent for the pair is 7022 ACD/P4ADGC, which matches the 25° angle, the P4S-class tolerancing and the duplex preloaded set. Same-envelope numbers with a different angle or preload are related sizes: a 2MM9122WI is the 15° version of the same bearing, and DUL and DUM suffixes are the light and medium preload variants of this set.