Fafnir3MM210WICRDUMSuper-Precision Angular Contact Ball Bearing 50 x 90 x 20 mm, 25°, Duplex Pair, Phenolic Cage

Product Description

What this part is

A Fafnir 3MM210WI-CR super-precision angular contact ball bearing, 50 mm bore by 90 mm outside diameter by 20 mm wide, supplied as a universally ground duplex pair. Fafnir is Timken’s super-precision spindle bearing line and the WI family is its single-row angular contact spindle bearing. The ISO equivalent envelope is the 7210 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. With no 9 ahead of the size block the bearing sits in the ISO 72 dimension series and the bore code 210 gives 50 mm. WI is the super-precision angular contact family, CR a phenolic cage riding on the outer ring land, and the DU block a duplex universally ground pair.

What these specs mean in practice

A 25° contact angle carries more thrust and less speed than the 15° version of the same size, which suits a spindle seeing real axial cutting load rather than maximum rpm. The one-piece phenolic cage riding on the outer land is light, quiet and self-lubricating, and it is what allows super-precision bearings to run at spindle speeds; it also sets a lower temperature ceiling than a brass cage.

Quantity and configuration

2 Pcs, one matched duplex pair. The rings are universally ground, so the pair mounts back-to-back, face-to-face or in tandem and the preload is set by the ground offsets rather than by shims.

Fitting notes

The pair is mounted with the marked faces together in the chosen arrangement and clamped fully against its shoulders, which is what brings the ground offset into play as preload. Shaft and housing fits for a P4S bearing are held much tighter than for general-purpose stock, and the bearing goes in clean and lubricated to its final specification.

Interchange guidance

An NSK 7210A5 or an SKF 7210 ACD/P4A in an equivalent duplex pair is the same specification. A 7210 in the 15° C angle or the 40° B angle is a related size in the same envelope rather than a substitution, since the split between radial and axial capacity moves with the angle. The Fafnir 2MM210WI is the 15° version of this size.