FafnirSuper-Precision Angular Contact Ball Bearing – Straight Bore, 40 mm ID, 90 mm OD, 23 mm Width, Open, ABEC 7/9 (P4S), CR Phenolic Outer-Land-Riding Cage.

Product Description

What this part is

Fafnir MM308WICR super-precision angular contact ball bearing, 300WI series. Brand: Fafnir (Timken). Part Number: MM308WICR. Bore: 40 mm. Outside Diameter: 90 mm. Overall Width: 23 mm. Design Units: Metric. Number Of Rows: 1. Rolling Elements: Ball. Bore Type: Straight. Closure Type: Open. Bearing Material: Chrome bearing steel.

Decoding the designation

Precision Class: P4S. Precision Rating: ABEC 7/9. The MM prefix is Fafnir’s super-precision spindle range and carries the P4S tolerance class. WI marks a low shoulder on both rings. CR is the phenolic outer-land-riding cage. Cage Material: Phenolic. Cage Type: CR – phenolic outer land riding. Series: 300WI, carrying the ISO 7308 envelope of 40 x 90 x 23 mm.

What these specs mean in practice

P4S is the tightest tolerance class Fafnir applies to a spindle bearing, holding bore, outside diameter and running accuracy close enough for a machine tool spindle where shaft runout sets the finish on the workpiece. The 300 series is the heavy section: a 40 mm shaft inside a 90 mm housing bore carries more load than a 70- or 72-series bearing on the same shaft. The phenolic cage rides on the outer ring land, staying centred at speed and holding lubricant against the ball pockets.

Quantity and configuration

Unit Quantity: 1 Pc.

Interchange guidance

Cross-Reference: Timken 7308, on the 40 x 90 x 23 mm envelope.

Designation variants

MPN Variants: MM308WICR, MM308WI, MM-308-WI-CR, MM 308 WI CR, 308WI, 7308-B, 7308 B T P4.