Fafnir2MM9105WIDUMSuper-Precision Angular Contact Ball Bearing 25 x 47 x 12 mm, 15°, Duplex Medium Preload

Product Description

What this part is

A Fafnir 2MM9105WI-DUM super-precision angular contact ball bearing, 25 mm bore by 47 mm outside diameter by 12 mm wide, supplied as a universally ground duplex pair at medium 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 7005 size.

Decoding the designation

The leading 2 in 2MM gives a 15° contact angle. The MM prefix denotes P4S precision, ABEC 7 on dimensional tolerances with ABEC 9 running accuracy. The 9 ahead of the size block places the bearing in the ISO 70 light dimension series and the bore code 05 gives 25 mm. WI identifies the super-precision angular contact family and DUM a duplex universally ground pair at medium preload.

What these specs mean in practice

A 15° contact angle is the high-speed choice: it carries less thrust and more speed than a 25° bearing of the same size, and it is what goes into grinding and high-rpm milling spindles. The ISO 70 light series keeps the outside diameter and section small for the bore, which lowers ball centrifugal loading and raises the speed ceiling further. Medium preload sits between the light setting used for maximum speed and the heavy setting used for maximum axial stiffness.

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 set by the ground ring offsets rather than by shims.

Fitting notes

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

Interchange guidance

An NSK 7005C or an SKF 7005 CD/P4A in an equivalent medium-preload duplex pair is the same specification. A 7005 in the 25° 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 3MM9105WI is the 25° version of this size.