FafnirMM9118KSuper Precision Deep Groove Ball Bearing 90x140x24 mm, Open, P4S Precision Class, 60 Light Series

Product Description

What this part is

A single-row deep groove ball bearing in the 6018 envelope — 90 mm bore, 140 mm outside diameter, 24 mm width — built to Fafnir’s MM super-precision standard. Open type, no shields or seals. The MM prefix is the important part: this is not a commercial 6018 but a spindle-grade bearing held to much tighter tolerance and runout limits.

Decoding the designation

MM — Fafnir super-precision prefix, which implies precision class P4S (ABEC 7/9 tolerances).
9118 — the 60 light dimension series with ISO bore code 18, giving a 90 mm bore: the 6018 envelope, 90 x 140 x 24 mm. The dimensions in the source data agree with the designation, so this part’s identity is internally consistent.
K — Fafnir configuration suffix carried on the carton; no published decode was located, so it is retained as a search term rather than translated into a spec.

Correcting the source data

The original listing described this bearing as “6018 P5 ABEC7”. P5 and ABEC 7 are two different classes — ABEC 7 corresponds to P4, not P5 — so the source contradicted itself. Because the MM prefix implies P4S, we have published P4S (ABEC 7/9) and dropped the P5 claim.

What these specs mean in practice

A deep groove bearing takes radial load with a useful amount of thrust in either direction, and needs no particular mounting orientation — which is why it is the default choice wherever an angular contact pair would be overkill. What P4S buys you is accuracy, not capacity: bore and outside diameter tolerance, width variation and radial and axial runout are all held to very close limits, so the shaft runs truer and the assembly generates less vibration and heat at speed.

The practical consequence is that this bearing is only worth fitting where the housing and shaft are machined to a matching tolerance. Dropped into a commercially bored housing, a P4S bearing gives you very little that a standard 6018 would not, because the fit error swamps the bearing’s own accuracy.

Open construction means lubrication and contamination exclusion are the housing’s job. That is normal for spindle work, where oil mist, oil-air or a controlled grease charge is supplied deliberately, but it makes this a poor choice for a dirty, unsealed position.

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 substituted the ratings of a commercial 6018 — different internal geometry and different class, so the figures would not apply. Contact Timken with the full designation if a certified rating is required.

Condition disclosure

Sealed in the factory bag, new old stock, with grease staining on the packaging. The bearing itself is unused.

Quantity and configuration

One bearing. There is no DU or SU suffix in the designation, so this is a plain single — it is not part of a matched or preload-ground set and does not need a partner.

Fitting notes

Handle by the rings and keep the bearing bagged until assembly; super-precision bearings are easily spoiled by airborne grit. Press only on the ring being fitted and never drive mounting force through the balls, which will brinell the raceways and destroy the running accuracy you paid for. Check the shaft and housing for burrs and confirm they are ground to a tolerance consistent with P4S before fitting.

Interchange guidance

The ISO base number is 6018. Legacy Fafnir MM numbers cross into Timken’s later super-precision numbering. Beware treating a commercial 6018 from any maker as an equivalent — it shares the envelope but is several tolerance classes coarser. Match on precision class as well as size.