Fafnir2MM215WIDULSuper-Precision Angular Contact Ball Bearing Pair – 75 mm Bore, 130 mm OD, 25 mm Width, 15° Contact Angle, Light Preload, Open

Product Description

What this part is

Fafnir 2MM215WI-DUL super-precision angular contact ball bearing, supplied as a matched duplex pair. Bore 75 mm, outside diameter 130 mm, width 25 mm per bearing, giving 50 mm across the mounted pair. Open on both faces, single row of balls in each bearing, phenolic outer-land-riding cage. This is a machine tool spindle bearing, built to super-precision tolerances rather than general-purpose bearing tolerances.

Decoding the designation

In the Fafnir super-precision scheme 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 215 is the ISO 7215 base number, the 72 medium dimension series. WI is the angular contact spindle configuration with the phenolic outer-land-riding cage. DU means the two rings are universally ground as a duplex pair, and the closing L sets light preload.

What these specs mean in practice

A 15° contact angle favours speed and radial stiffness over thrust capacity. A 25° bearing in the same envelope carries more axial load and runs slower, so the two are not interchangeable in a spindle stack. Light preload is the low-heat, high-speed choice; medium preload trades running speed for axial rigidity. The phenolic outer-land-riding cage is light, tolerates oil-mist and grease lubrication, and is the reason this series runs at spindle speeds.

Preload rather than clearance

Universally ground duplex pairs are supplied with the offset ground into the ring faces, so preload is established the moment the pair is clamped up. 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 the pair to be mounted back-to-back, face-to-face or in tandem; back-to-back and face-to-face give the stated light preload, tandem shares radial load in one thrust direction.

Fitting notes

Corner fillet radius on the shaft and housing shoulders is 1.5 mm maximum. Ring faces are ground flat and the pair is matched, so the two bearings are mounted together and in their marked relative orientation. Clamping is against the ring faces, not through the cage.

Interchange guidance

The SKF 7215 CD/P4ADGA and NSK 7215CTYNDULP4 are same-specification universally ground 15° light-preload pairs. The 2MM215WI-DUM in the same envelope is a medium-preload set and the NSK 7215A5 equivalents are 25°, so both are related sizes rather than direct substitutions.