Fafnir2MM210WIDUMSuper-Precision Angular Contact Ball Bearing Pair – 50 mm Bore, 90 mm OD, 20 mm Width, 15° Contact Angle, Medium Preload, Open

Product Description

What this part is

Fafnir 2MM210WI-DUM super-precision angular contact ball bearing, supplied as a matched duplex pair. Bore: 50 mm (1.9685 in). Outside diameter: 90 mm (3.5433 in). Width: 20 mm (0.7874 in) per bearing. Total width: 40 mm (1.5748 in) across the mounted pair. Open on both faces, one row of balls per bearing, phenolic outer-land-riding cage. This is a machine tool spindle bearing held to super-precision tolerances.

Verified performance data

Contact angle: 15°.

Dynamic radial load rating C1: 47,400 N (10,700 lbf) per bearing.

Static radial load rating C0: 31,700 N (7,130 lbf) per bearing.

Limiting speed, grease: 16,000 rpm.

Limiting speed, oil: 32,000 rpm.

Precision class: ABEC 7/9, ISO P4S.

Cage type: Phenolic, outer-land-riding.

Rolling elements: Steel balls.

Bore type: Straight.

Seal type: Open.

Decoding the designation

The leading 2MM gives a 15° contact angle and the MM prefix places the bearing in the P4S super-precision class, equivalent to ABEC 7/9. The 210 is the ISO 7210 base number in the 72 medium dimension series. WI is the angular contact spindle configuration and CR identifies the phenolic outer-land-riding cage. DU means the rings are universally ground as a duplex pair, and the closing M sets medium preload.

What these specs mean in practice

Medium preload sits between the light and heavy classes: more axial and radial rigidity than light preload, less internal friction and heat than heavy. It is the usual choice for general machine tool spindles that see both cutting thrust and speed. The 15° contact angle favours speed and radial stiffness; a 25° bearing in this envelope carries more thrust and runs slower.

Preload and clearance

Internal clearance: preloaded, medium preload ground into the ring faces at manufacture and established as soon as the pair is clamped.

Quantity and configuration

Two bearings, one matched duplex pair, ground as a set. Universal grinding allows back-to-back, face-to-face or tandem mounting; back-to-back and face-to-face give the stated medium preload, tandem shares radial load in a single thrust direction.

Mounting data

The outer rings carry V marks that identify the intended arrangement. Shaft and housing seats are held to precision tolerances. Lubricant: grease or oil, suited to the phenolic cage.

Interchange guidance

The SKF 7210 CD/P4ADGB, FAG B7210-C-T-P4S-DUM and NSK 7210CTYNDUMP4 are same-specification universally ground 15° medium-preload pairs. The 25° versions of the same envelope, such as the SKF 7210 ACD and FAG B7210-E, are related sizes: the contact angle changes the thrust-to-speed balance, so they are not a like-for-like swap.