Fafnir2MM210WIDUHSuper-Precision Angular Contact Ball Bearing Pair – 50 mm Bore, 90 mm OD, 20 mm Width, 15° Contact Angle, Heavy Preload, Open

Product Description

What this part is

Fafnir 2MM210WI-DUH super-precision angular contact ball bearing, supplied as a matched duplex pair. Bore 50 mm, outside diameter 90 mm, width 20 mm per bearing, giving 40 mm across the mounted pair. Open on both faces, one row of balls per bearing, phenolic outer-ring-guided cage. This is a machine tool spindle bearing held to super-precision tolerances.

Decoding the designation

The leading 2MM gives a 15° contact angle and the MM prefix places the bearing in the P4S super-precision class, equivalent to ABEC 7/9. The 210 is the ISO 7210 base number in the 72 medium dimension series. WI is the angular contact spindle configuration with the phenolic outer-ring-guided cage. DU means the rings are universally ground as a duplex pair, and the closing H sets heavy preload.

What these specs mean in practice

Heavy preload is the stiff end of the range. It raises axial and radial rigidity and holds spindle position under interrupted cutting loads, at the cost of more internal friction, more heat and a lower practical speed than the light and medium classes. The 15° contact angle keeps speed capability high for a preloaded set; a 25° bearing in the same envelope would carry more thrust and turn slower.

Preload rather than clearance

The preload offset is ground into the ring faces at manufacture, so it is established as soon as the pair is clamped. A radial internal clearance grade does not apply to a preloaded set, and none is published here.

Quantity and configuration

Two bearings, one matched duplex pair, ground as a set. Universal grinding allows back-to-back, face-to-face or tandem mounting; back-to-back and face-to-face give the stated heavy preload, tandem shares radial load in a single thrust direction.

Interchange guidance

The SKF 7210 CD/P4ADGC and NSK 7210CTRDUHP4 are same-specification universally ground 15° heavy-preload pairs. Light and medium preload versions of the same 2MM210WI, and 25° equivalents such as the NSK 7210A5 family, are related sizes rather than direct substitutions.