FafnirSuper Precision Spindle Angular Contact Ball Bearing 20x47x14 mm, 25 Degree Contact Angle, Phenolic Outer-Land-Riding Cage, Duplex Universal Light Preload, ISO P4S

Product Description

What this part is

A Fafnir super-precision spindle angular contact ball bearing, 20 mm bore × 47 mm outside diameter × 14 mm width, 25° contact angle, ground to duplex universal light preload. Mounted as a back-to-back pair the set occupies 28 mm of shaft length. Fafnir is now part of Timken, and the MM-prefix spindle range remains in current production.

Decoding the designation

3MM denotes a super-precision spindle bearing at the high contact angle, 25°: Timken’s own catalogue footnote states that 3 is the Timken designation and E is the ISO designation for 25°, and 2MM is the corresponding 15° series. 204 is the 72-series bore code, 20 mm bore in the 47 mm outside diameter envelope. WI is Timken’s angular contact geometry code: full shoulders both sides of the inner ring and a low shoulder on the outer ring, so the bearing carries thrust in one direction and is non-separable. CR is a composition (phenolic) cage riding on the outer-ring land, standard service to 93 °C. DUL is a flush-ground duplex pair at light preload; DUM is medium, DUH heavy, DUX extra-light, and SUL is the single flush-ground equivalent.

Precision class — what MM buys

The MM prefix denotes ISO P4S, which is not the same as P4. Timken’s specification is that running accuracy and performance meet ABEC 9 (ISO P2) levels while other features conform to ABEC 7 (ISO P4) requirements, so the running accuracy is a class higher than the dimensional tolerance. Precision Class: P4S.

What these specs mean in practice

25° with light preload is the middle-ground spindle specification: meaningfully more thrust capacity and axial stiffness than a 15° bearing, but preloaded lightly so it still turns fast and runs cool. It suits milling and machining-centre spindles that see real cutting thrust but also need speed. The phenolic cage rides on the outer-ring land, damps ball-passage excitation, tolerates marginal lubrication far better than steel or brass, and is what makes very high dN values practical; its limit is temperature, 93 °C. Contact Angle: 25°. Cage Material: Phenolic. Dynamic Load Rating: 15,500 N (3,490 lbf). Static Load Rating: 7,700 N (1,730 lbf). Rolling Elements: 10 balls, 7.94 mm diameter. Preload Force: 130 N (DUL). Limiting Speed: 32,100 rpm single bearing; DUL pair mounted back-to-back 25,740 rpm grease / 43,740 rpm oil.

Mounting data

Preload Force: 130 N as a DUL set. Assembled duplex pair width: 28 mm. Cage service temperature limit: 93 °C.

Quantity and configuration

DUL denotes a flush-ground duplex universal pair at light preload; assembled pair width is 28 mm.

Interchange guidance

The ISO world number for this bearing is 7204E-T-P4S-DUL: E for 25°, T for the phenolic machined cage, P4S for the Fafnir MM precision spec. Schaeffler format is B7204-E-T-P4S-DUL. The 15° sibling in the same envelope is 2MM204WI CR DUL and is not interchangeable, since it carries a different contact angle and different ratings. Fafnir spindle bearings are now sold under the Timken brand.