FafnirSuper-Precision Deep Groove Ball Bearing 40x80x18 mm, Machined Bronze Cage, ISO P4S, Open

Product Description

What this part is

A Fafnir spindle-grade deep groove ball bearing in the 200K series, size 208: 40 mm bore, 80 mm outside diameter, 18 mm width. In inch terms that is 1.5748 in bore, 3.1496 in outside diameter, 0.7087 in width. It is a Conrad-type single-row radial ball bearing, ground to super-precision tolerances and fitted with a machined bronze cage, open on both faces. The 200K series occupies the ISO 62-series envelope, so the size corresponds dimensionally to a 6208.

Decoding the designation

MM denotes the Fafnir super-precision spindle grade, ISO P4S (ABEC 7/9). 208 is the 200K series, bore code 08: the 40 x 80 x 18 mm envelope. K is the Fafnir internal design code for the spindle deep groove family. MBR denotes a machined bronze cage.

What these specs mean in practice

A deep groove Conrad geometry carries radial load as its primary duty and takes axial load from either direction through the shoulder contact, which makes it the standard choice for the non-thrust end of a precision spindle and for locations where a single bearing must hold a shaft in both directions. Super-precision grinding to P4S holds bore, outside diameter and raceway runout an order tighter than a commercial P0 bearing, so the achievable spindle concentricity is set by the shaft and housing rather than the bearing. A machined bronze cage is dimensionally stable, tolerates higher temperatures than a polymer or phenolic cage, and handles marginal lubrication and shock loading better, at the cost of extra rotating mass and a lower speed ceiling than a phenolic cage of the same size.

Published specifications

Bore d: 40 mm (1.5748 in). Outside diameter D: 80 mm (3.1496 in). Width B: 18 mm (0.7087 in). Basic dynamic radial load rating C: 36.2 kN (8,130 lbf). Basic static radial load rating C0: 20.0 kN (4,500 lbf). Precision class: ISO P4S (ABEC 7/9). Cage: machined bronze. Rolling elements: steel balls. Rows: single row. Closure: open both faces. Maximum shaft fillet radius: 1 mm (0.039 in). Shaft backing shoulder diameter: 47.2 mm (1.860 in). Housing backing shoulder diameter: 73.2 mm (2.880 in).

Quantity and configuration

Single bearing, 1 Pc.

Fitting notes

The bore is cylindrical and mounts on a ground journal to an interference fit appropriate to the P4S bore tolerance. Backing shoulder diameters of 47.2 mm on the shaft and 73.2 mm in the housing clear the ring corners with a 1 mm fillet radius; abutment faces square to the axis are what preserve the ground running accuracy once clamped. Being a deep groove design it locates the shaft axially in both directions without a second bearing set against it.

Interchange guidance

Dimensionally this is the ISO 6208 envelope, so a commercial 6208 shares bore, outside diameter and width but not the tolerance class or cage. Within the Fafnir scheme the corresponding standard-tolerance bearing is the 208K, and the phenolic inner-land-riding version is the MM208KCR. Related sizes in the same 40 x 80 x 18 mm envelope with a different cage, tolerance class, clearance or closure — 6208, 6208-2RS, MM208KCR, 208K — are different parts.