Fafnir3MM208WICRSuper Precision Angular Contact Ball Bearing 40x80x18 mm, 25° Contact Angle, Phenolic Cage, ABEC 7, Universally Ground

Product Description

What this part is

A Fafnir 3MM208WI super-precision angular contact ball bearing with a phenolic cage, 40 mm bore x 80 mm outside diameter x 18 mm wide — the 7208 envelope. The outer ring is counterbored on one side so the full ball complement can be loaded and so the bearing develops a contact angle. It carries radial load plus thrust in one direction, and the high shoulder must face the thrust.

Decoding the designation

3 – in Timken/Fafnir super-precision numbering the numeric prefix names the contact angle: 3MM = 25°, 2MM = 15°.
MM – Fafnir super-precision tolerance, ABEC 7; the MM prefix implies the P4S tolerance package. A single M would be ABEC 3.
208 – 200 series, bore code 08, so 40 mm bore.
WI – maximum-capacity (filling-slot) type with a counterbored outer ring, which is what makes it angular contact rather than deep groove.
CR – composition retainer: a phenolic laminated-fabric, outer-land-riding cage.

What these specs mean in practice

25° is the middle of the contact-angle range and the most broadly useful choice. Against a 15° bearing it gives noticeably more thrust capacity and axial stiffness; against a 40° bearing it gives more speed capability and less heat. If your spindle sees real cutting thrust as well as speed — boring heads, milling spindles, precision drive shafts —25° is usually the right answer, and it is why 3MM is the most commonly stocked Fafnir super-precision prefix.

ABEC 7 controls bore, outside diameter, width and above all radial and axial runout, so the ring can be fitted in any rotational orientation without hunting a high spot. The phenolic outer-land-riding cage is the high-speed complement: light, self-lubricating, quiet, and soft enough that a ball skid polishes the pocket instead of galling it. Its limits are sustained heat much above roughly 120 °C and attack by some synthetic lubricants and solvents.

Published dimensions

Bore (d): 40 mm
Outside diameter (D): 80 mm
Width (B): 18 mm
Contact angle: 25°
Rows: 1
Cage: phenolic laminated fabric, outer-land riding (CR)
Precision: ABEC 7
Closure: open, no seals or shields
Outer ring: counterbored one side

Quantity and configuration

Sold as one bearing. This is a single, not a factory-matched duplex set, so no preload is supplied. The WI series is universally ground, so two can be clamped face-to-face, back-to-back or in tandem and will develop a repeatable preload; where a drawing calls for a matched pair to a named preload class, order a DUL, DUM or DUH set.

Fitting notes

Orient the counterbored (low shoulder) side away from the thrust load — fitted backwards the balls climb the raceway shoulder and the bearing fails fast. Press or induction-heat against the inner ring only; never hammer an ABEC 7 bearing and never drive force through a phenolic cage. Grease sparingly, roughly a quarter to a third fill, or run the oil-air system the spindle was designed around. A single angular contact locates the shaft one way only and needs an opposing bearing in the arrangement.

Interchange guidance

Fafnir is now sold by Timken. Direct 40 x 80 x 18 mm super-precision 25° equivalents: NSK 7208A5TYNP4 (NSK A5 is 25°), SKF 7208 ACD/P4A (SKF AC is 25°), RHP 7208ETP4 (RHP E is 25°), FAG B7208-E-T-P4S (FAG E is 25°). Carried as dimensionally-correct cross-references with the difference named: NSK 7208A is the same envelope but NSK A is 30°, not 25°; NSK 7208CTYNP4 and NTN 7208CT1P4 are the same envelope at 15°; FAG 7208-B-TVP-P4 is 40°. The B7208-E-T-DUL-P4 form that has travelled with this record names a duplex pair rather than a single bearing, so it is kept as a search term only — this listing is one bearing. Within Fafnir, 2MM208WI is this bearing at 15°.