FafnirMM306WI2Super-Precision Angular Contact Ball Bearing – 30 mm ID, 72 mm OD, 19 mm Width, Straight Bore, Open, Machined Phenolic Cage, P4S

Product Description

What this part is

Fafnir MM306WI-2 super-precision angular contact ball bearing, 30 mm bore, 72 mm outside diameter, 19 mm width. Straight bore, open on both faces, chrome steel rings and balls with a machined phenolic cage. Timken catalogues the 300WI series as spindle angular contact ball bearings alongside the 9100WI, 9300WI and 200WI families.

Decoding the designation

MM is Timken’s super-precision spindle prefix and carries the P4S precision class, ABEC 7/9. 306 gives bore code 06 for the 30 mm bore in the 300WI heavy dimension series. WI is the series designation. CR is the machined phenolic outer-land-riding cage.

What these specs mean in practice

An angular contact ball bearing takes combined radial and axial load along a contact line inclined to the bearing axis, so it supports a spindle in one thrust direction and is normally mounted against a second bearing to locate the shaft both ways. P4S holds running accuracy tighter than P4 on the critical raceway and face tolerances, which is what keeps spindle runout low at speed. The machined phenolic cage is light, self-lubricating and low friction, and suits oil, oil-air or light grease lubrication in a 72 mm envelope.

Bore form

Straight cylindrical bore, mounted on an interference fit shaft seat with the outer ring located in a bored housing.

Interchange guidance

The 30 x 72 x 19 mm envelope corresponds to the ISO 306 heavy series. A 2MM306WI in the same envelope is the 15° execution and a 3MM306WI the 25° execution, making both related sizes rather than interchanges, since the contact angle changes how thrust and speed are balanced.