Fafnir3MM309WICRDULSuper-Precision Angular Contact Ball Bearing 45 x 100 x 25 mm, 25°, Duplex Light Preload, Phenolic Cage

Product Description

What this part is

A Fafnir 3MM309WI-CR-DUL super-precision angular contact ball bearing, 45 mm bore by 100 mm outside diameter by 25 mm wide, supplied as a universally ground duplex pair at light preload. Fafnir is Timken’s super-precision spindle bearing line and WI is its single-row angular contact spindle family. The ISO equivalent envelope is the 7309 size.

Decoding the designation

The leading 3 in 3MM gives a 25° contact angle. The MM prefix denotes P4S precision, ABEC 7 on dimensional tolerances with ABEC 9 running accuracy. The size block 309 places the bearing in the ISO 73 medium dimension series with a bore code of 09 for 45 mm, which is why the outside diameter and width are heavier than a 7209 of the same bore. CR is a phenolic cage riding on the outer ring land and DUL a duplex universally ground pair at light preload.

What these specs mean in practice

The 73 medium series puts more material and larger balls into the same bore than the 72 series, which raises both radial and axial capacity at the cost of speed. The 25° angle biases that capacity toward thrust. Light preload is the setting chosen where speed and heat generation matter more than axial stiffness, and it is the usual choice for the drive end of a spindle running long cycles.

Quantity and configuration

2 Pcs, one matched duplex pair. Universally ground rings allow back-to-back, face-to-face or tandem mounting, with the preload established by the ground ring offsets.

Fitting notes

The marked faces go together in the chosen arrangement and both rings are clamped fully against their shoulders, which is what converts the ground offset into preload. Fits on a P4S bearing are held far tighter than on general-purpose stock, and the bearing is fitted clean and lubricated to its final grease or oil specification.

Interchange guidance

An NSK 7309A5 or an SKF 7309 ACD/P4A in an equivalent light-preload duplex pair is the same specification. A 7309 in the 15° C angle or the 40° B angle is a related size in the same envelope rather than a substitution. A 7209 shares the 45 mm bore but is a lighter series with a smaller outside diameter and different capacity.