Fafnir3MM9122Super Precision Angular Contact Ball Bearing 110x170x28 mm, 25° Contact Angle, P4S Precision Class, Open, Single

Product Description

What this part is

A super-precision angular contact ball bearing in the 7022 envelope — 110 mm bore, 170 mm outside diameter, 28 mm width — built to Fafnir’s MM spindle-bearing standard. Open type, 25° contact angle.

Decoding the designation

3MM — Fafnir super-precision prefix carrying a 25° contact angle. The companion 2MM prefix is 15°.
MM prefix — implies precision class P4S (ABEC 7/9), not plain P4.
9122 — the 70 dimension series with ISO bore code 22, giving a 110 mm bore: the 7022 envelope, 110 x 170 x 28 mm. Designation and dimensions agree.
No DU or SU suffix — this designation carries no duplex or universal-grinding code, so it is a plain single bearing rather than half of a preload-matched pair.

Correcting the source data

The original listing cross-referenced this bearing as “7022-A”. In NSK’s scheme — the scheme that 7022-style suffixes are usually read in — A denotes a 30° contact angle, while A5 denotes 25°. Since the 3MM prefix fixes this bearing at 25°, the correct NSK-scheme cross-reference is 7022A5, not 7022A. The carton markings recorded against this item include “7022 A5T P4”, which agrees with 25° and confirms the correction. We have published 7022A5 and demoted the 7022A form to a search term only.

This is not a pedantic distinction. A 30° bearing substituted into a spindle designed for 25° changes the load path, the stiffness and the speed limit of the whole assembly.

What these specs mean in practice

A 25° contact angle carries considerably more thrust per unit of radial load than a 15° bearing and holds axial position better under interrupted cutting, at the cost of a lower speed ceiling and more heat generated at a given rpm. It is the usual choice for milling and boring spindles; 15° is the usual choice for grinding and high-speed work. Substituting one for the other changes the machine’s stiffness and thermal behaviour, so check the builder’s specification first.

Published ratings and mounting data

No dynamic or static load rating and no limiting speed is published for this legacy Fafnir designation by a source we will stand behind, so those cells are deliberately blank. We have not borrowed figures from the 2MM9122 (15°) or from a commercial 7022 — different angle and different class, so the numbers would not apply. Contact Timken with the full designation if a certified rating is required.

Quantity and configuration

One bearing, sold as a single. Note that angular contact bearings are directional: a single one takes thrust in one direction only and must be opposed by something else in the assembly. If you need two bearings ground as a matched preloaded pair, that is a different designation (3MM9122WI-DUL or -DUM) and this part will not substitute for it.

Fitting notes

Observe the thrust direction marking on the outer ring — fitting an angular contact bearing backwards loads it on the unsupported shoulder and will fail it quickly. Press only on the ring being fitted, never through the balls, and confirm the shaft and housing are ground to a tolerance consistent with P4S, or the bearing’s accuracy is wasted.

Interchange guidance

ISO base number 7022. Suffix letters for contact angle differ by maker: Timken reads C as 15° and E as 25°; NSK reads C as 15°, A5 as 25° and A as 30°; SKF reads AC as 25°. Always establish which scheme a candidate number is written in before treating it as an equivalent. Two other 7022-envelope bearings are in our stock in different brands and precision classes — ask if you need a specific angle, class or preload.