FafnirMM318KSuper Precision Deep Groove Ball Bearing, 90 x 190 x 43 mm, 63 Heavy Series, P4S Precision Class, Open

Product Description

What this part is

Fafnir MM318K super-precision deep groove ball bearing. Bore: 90 mm. Outside Diameter: 190 mm. Width: 43 mm. ISO base number: 6318. Precision Class: P4S (ABEC 7/9). Series: 63 heavy dimension series. Number of Rows: 1. Rolling Elements: balls. Closure: open. Design Units: metric. Fafnir super-precision production passed to The Timken Company.

Decoding the designation

MM is Fafnir’s super-precision spindle-bearing prefix and carries precision class P4S, ABEC 7/9.

3 is the 63 heavy dimension series. 18 is the ISO bore code, which is a 90 mm bore, placing the bearing in the 6318 envelope at 90 x 190 x 43 mm.

K is a Fafnir configuration suffix carried on the carton and retained as a searchable term.

What these specs mean in practice

A super-precision deep groove bearing suits a position that needs deep-groove load behaviour — radial load with modest thrust in either direction — together with the running accuracy of a spindle bearing. P4S holds bore and outside diameter tolerance, width variation and radial and axial runout to close limits, so the shaft runs truer and the assembly generates less vibration at speed. That is why these go into grinding and boring spindles, precision gearboxes and instrument drives.

The 63 heavy series carries more load in the same bore than the equivalent 62 or 60 series, because it is wider and larger in outside diameter with bigger balls. It trades speed capability and radial space for capacity.

Fitting notes

A P4S bearing delivers its accuracy in a housing and on a shaft machined to matching tolerance. Handling is by the rings, with the bearing kept in its wrapper until assembly, and mounting force applied evenly to the ring being pressed.

Quantity and configuration

Unit Quantity: 1 bearing, open, single row.

Interchange guidance

ISO base number: 6318, 90 x 190 x 43 mm. Legacy Fafnir MM numbers cross to Timken’s later super-precision numbering. A commercial-grade 6318 is a related size at a coarser tolerance class, so precision class is matched as well as envelope. Also written MM318K, MM-318-K, MM 318 K, M318K, M-318-K, MM318 and 318K.