Fafnir2MM210WIDUMSuper-Precision Angular Contact Ball Bearing Pair – 50 mm Bore, 90 mm OD, 20 mm Width, 15° Contact Angle, Medium Preload, Open

Product Description

What this part is

Fafnir 2MM210WI-DUM 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-land-riding 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 and CR identifies the phenolic outer-land-riding cage. DU means the rings are universally ground as a duplex pair, and the closing M sets medium preload.

What these specs mean in practice

Medium preload sits between the light and heavy classes: more axial and radial rigidity than light preload, less internal friction and heat than heavy. It is the usual choice for general machine tool spindles that see both cutting thrust and speed. The 15° contact angle favours speed and radial stiffness; a 25° bearing in this envelope carries more thrust and runs 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 medium preload, tandem shares radial load in a single thrust direction.

Interchange guidance

The SKF 7210 CD/P4ADGB, FAG B7210-C-T-P4S-DUM and NSK 7210CTYNDUMP4 are same-specification universally ground 15° medium-preload pairs. The 25° versions of the same envelope, such as the SKF 7210 ACD and FAG B7210-E, are related sizes: the contact angle changes the thrust-to-speed balance, so they are not a like-for-like swap.