FafnirRM209WICRPrecision Angular Contact Ball Bearing, 45 x 85 x 19 mm, Counterbored Outer Ring, Phenolic Cage, ABEC 3, Open

Product Description

What this part is

A Fafnir RM209WI precision angular contact ball bearing with a composition (phenolic) cage, 45 mm bore x 85 mm outside diameter x 19 mm wide — the 7209 / 209 envelope. The outer ring is counterbored on one side so the ball complement can be loaded and so the bearing develops a contact angle: it therefore takes radial load plus thrust in one direction, and the high shoulder must face the thrust.

Decoding the designation

R – Fafnir prefix for regular internal fit-up (as opposed to H snug, P loose or J extra-loose).
M – ABEC 3 tolerance class. Note that in Fafnir nomenclature a single M is ABEC 3, a doubled MM is the ABEC 7 super-precision grade, and M with an FS6xxxx suffix is ABEC 5. It is a one-letter difference with three different answers, and it is the single most misread element of Fafnir numbering.
209 – 200 series, bore code 09, 45 mm bore.
WI – maximum-capacity (filling-slot) type with the outer ring counterbored, which is what makes the bearing angular contact rather than deep groove.
CR – composition retainer, i.e. a phenolic laminated-fabric cage. Fafnir stamps CR on the carton rather than on the ring, so the bearing itself may read only RM209WI.

What these specs mean in practice

A phenolic cage is chosen for one reason: it runs quiet and cool at speed. It is light, so cage inertia is low; it is self-lubricating, so it survives marginal lubrication; and it is soft enough that a ball skid polishes the pocket instead of galling. The trade-off is temperature and chemistry — phenolic does not like sustained heat much above about 120 °C, and some synthetic lubricants and solvents attack it. Check the cage material against your lubricant before fitting.

ABEC 3 is a step above standard tolerance on bore, outside diameter, width and runout. It is the grade used for machine spindles and precision gear drives that need repeatable location but are not running at super-precision speeds — if your machine drawing calls for ABEC 5 or ABEC 7, this bearing is the wrong class even though the envelope is identical. Regular fit-up (the R prefix) means standard internal radial clearance rather than a preload-selected or loose class.

Published dimensions

Bore (d): 45 mm
Outside diameter (D): 85 mm
Width (B): 19 mm
Rows: 1
Cage: phenolic / laminated fabric composition (CR)
Precision: ABEC 3
Internal fit-up: regular (R)
Closure: open, no seals or shields
Outer ring: counterbored one side

Quantity and configuration

Sold as one bearing. This is a single, not a matched duplex set — there is no ground offset in the faces and no supplied preload, so two of these clamped together will not produce a defined preload the way a DU-suffixed pair does. Where a spindle drawing calls for a matched pair, order a DU, DUL, DUM or DUH set.

Fitting notes

Orient the bearing so the counterbored (low shoulder) side faces away from the thrust load — fitted backwards the balls climb out of the raceway shoulder and the bearing fails quickly. Press or heat onto the shaft against the inner ring only; never drive load through the balls, and never through a phenolic cage. Grease sparingly — roughly a third fill is right for a counterbored angular contact at speed. Because a single angular contact locates the shaft in one direction only, it needs an opposing bearing somewhere in the arrangement.

Interchange guidance

Fafnir bearings are now sold by Timken, so Timken RM209WICR and Fafnir RM209WICR are the same part. Same-envelope 45 x 85 x 19 mm single-row angular contact equivalents, with the differences that matter named: NSK 7209CTYNP5 and 7209A5TYNP5 (C is NSK’s 15° code, A5 is 25°), SKF 7209 ACD/P4A (AC is SKF’s 25° code), FAG 7209B.TVP.P5 (B is FAG’s 40° code), NTN 7209CT1P5 (C is NTN’s 15° code). All four sit in the same envelope but each names a different contact angle and precision class, so use them as dimensional cross-references and match the angle your spindle was designed around. The 7209-B and 7209 T P4 designations that have travelled with this record are carried here as searchable references rather than as published specifications for this bearing.