Fafnir3MM209WIDUHSuper Precision Angular Contact Ball Bearing, Duplex Pair, 45 x 85 x 19 mm, 25° Contact Angle, Heavy Preload, Phenolic Outer-Land-Riding Cage, ABEC 7/9

Product Description

What this part is

A super precision angular contact ball bearing for machine tool spindles, 45 mm bore by 85 mm outside diameter by 19 mm wide per bearing, supplied as a universally ground duplex pair with heavy preload. It is a spindle bearing, not a general-purpose or automotive ball bearing: the raceway geometry, cage and tolerance grade all exist to hold a shaft concentric at speed under a combined radial and axial load.

Decoding the designation

3MM — Fafnir/Timken super precision metric series with a 25° contact angle.
209 — 200WI dimension series, 45 mm bore.
WI — the standard Fafnir super precision spindle angular contact ball bearing series.
CR — phenolic outer-land-riding cage (Timken designation MBR). This appears on the carton and in Timken’s own manufacturing part number even when a title omits it.
DU — duplex universally ground, so the two rings are ground to mount as a matched pair in any orientation without shims.
H — heavy preload.
MM prefix — implies ISO P4S (ABEC 7/9), not P4.

Correcting the source data

The listing previously cross-referenced this bearing to 7209-A and to a world number ending P4. Timken’s own catalogue publishes the world part number as 7209E-T-P4S-DUH. In this scheme the E denotes the 25° contact angle and the T denotes the phenolic cage, and the MM prefix carries P4S rather than P4 — so the P4 form was the error, not the MM number. The 7209A form is retained below as a search term only, not as a Timken-published equivalent. An unsupported “Manufactured in the United States” claim has also been removed: nothing in the published data or the carton markings establishes an origin, and Fafnir cartons have read England.

What these specs mean in practice

The 25° contact angle is the deciding spec. Against the 15° version of the same envelope — 2MM209WI — the steeper angle carries substantially more thrust and gives a stiffer axial response, which is what you want on a spindle that takes heavy cutting loads or a screw-driven axis. What it trades away is speed: a steeper angle raises ball spin and cage load, so the limiting speed and the heat generated at a given rpm are both worse than the 15° part. Choose 25° for rigidity, 15° for rpm.

Heavy preload compounds that trade-off. It removes essentially all axial play and maximises stiffness and running accuracy, at the cost of higher internal friction, more heat and shorter grease life than a light or medium preload set. Do not substitute a DUL or DUM set into a spindle designed around DUH, or the axial stiffness the machine was designed around disappears.

The phenolic outer-land-riding cage is the high-speed feature. Phenolic is light and self-lubricating, so it generates far less heat than a steel cage, and riding on the outer ring land lets centrifugal force stabilise the cage rather than fight it. It is also the reason this bearing must never be cleaned with solvents that attack phenolic, and why it should not be run dry.

Published ratings and mounting data

Contact angle: 25°
Precision: ISO P4S (ABEC 7/9)
Preload: heavy
Bore 45 mm, outside diameter 85 mm, width 19 mm per bearing, total width 38 mm as a pair
Dynamic radial load rating C1, 1 million revolutions, duplex set: 9,700 lbf / 43,100 N
C1 ISO dynamic radial rating per row: 8,820 lbf / 39,200 N
Static radial load rating C0: 6,200 lbf / 27,600 N
Limiting speed, grease: 17,200 rpm
Limiting speed, oil: 31,600 rpm
Maximum shaft fillet radius: 1 mm
Shaft backing shoulder diameter: 52.3 mm
Housing backing shoulder diameter: 78.2 mm
Outer ring “to clear” radius: 1 mm

Ratings and mounting data above are from Timken’s own published catalogue data for 3MM209WICRDUH. They are specific to the 25° 3MM variant; the 15° 2MM209WI carries different ratings and the two must not be interchanged on paper.

Quantity and configuration

DUH is a duplex pair, so the sale unit is two bearings ground and matched to each other as a set. They are supplied and priced as one set and cannot be split without losing the matched preload. Confirm the count on arrival if your application depends on it: duplex sets do get separated in surplus handling, and a matched pair is only worth its preload while both rings stay together.

Fitting notes

Universally ground rings mean the pair can be mounted back-to-back, face-to-face or in tandem, but the ground faces must be assembled in the orientation the machine calls for and clamped square. Preload is developed by clamping the ground faces solidly together, so any burr, dirt film or non-square abutment on the shaft or housing shoulder directly corrupts the preload the set was ground to deliver. Respect the 52.3 mm shaft and 78.2 mm housing backing shoulder diameters and the 1 mm fillet clearance. Handle by the outer ring, keep the pair in its packaging until the moment of assembly, and follow a proper run-in before applying full speed.

Interchange guidance

Timken’s published world equivalent is 7209E-T-P4S-DUH. Same-envelope bearings from other makers in a 25°, P4S, phenolic-cage, heavy-preload duplex execution are functionally comparable, but contact angle, preload class and cage material must all match — a 15° or a steel-cage substitute is a different bearing in the same box size. Fafnir super precision bearings are now sold under the Timken brand; Fafnir and Timken numbers of this form are the same product line.