FafnirMM135EXCRDUAngular Contact Ball Bearing – 1-1/4 in ID, 2-11/16 in OD, 5/8 in Width, Open, Phenolic Cage, ABEC 7/9 P4S

Product Description

What this part is

Fafnir MM135EXCRDU-20 is a super-precision angular contact spindle bearing from Timken’s Ex-Cell-O series, supplied as a duplex universal pair. Bore Diameter: 1.2500 in (31.750 mm). Outside Diameter: 2.6875 in (68.263 mm). Overall Width: 0.6250 in (15.875 mm). Total Width: 1.2500 in (31.750 mm) for the pair. Bore Type: Straight. Closure Type: Open. Rolling Elements: Ball. Number Of Rows: 1 per bearing. Cage Material: Phenolic. Bearing Material: Bearing steel.

Decoding the designation

MM — Timken Fafnir super-precision grade P4S. Timken’s Machine Tool Catalog sets P4S running accuracy at ABEC 9 / ISO P2 while holding the remaining bearing features at ABEC 7 / ISO P4.

EX — the Ex-Cell-O series, built on Timken WI construction and dimensioned for inch-nominal machine tool spindles, with bore and outside-diameter tolerances held nominal to plus.

135 — the Ex-Cell-O reference number for this size.

CR — phenolic composition cage, Timken’s standard cage for super-precision spindle bearings. Phenolic is light and self-lubricating, which is what allows the high speeds these bearings run at.

DU — duplex universal. Two bearings ground as a matched set with flush faces, so the pair mounts back to back, face to face or in tandem.

20 — a Fafnir variant code. Under the Fafnir lettering system a one- or two-digit suffix marks a bearing built to a specification differing from the catalogue standard.

What these specs mean in practice

Precision Class: ABEC 7/9 / P4S. Super-precision grinding holds bore, outside diameter and raceway running accuracy far tighter than a standard-class bearing, which is what keeps spindle runout and running vibration low at speed.

Cage Material: Phenolic. A machined phenolic cage weighs a fraction of a steel one, so cage inertia and ball-pocket loading stay low as the bearing spins up.

The EX series exists so that an inch-nominal Ex-Cell-O spindle seat takes a current-production Timken bearing. The nominal-to-plus tolerance bias on bore and outside diameter is what matches the original inch fit.

Mounting data

Bore Diameter: 1.2500 in (31.750 mm). Outside Diameter: 2.6875 in (68.263 mm). Overall Width: 0.6250 in (15.875 mm). Total Width: 1.2500 in (31.750 mm) as a duplex pair. Bore Type: Straight.

Quantity and configuration

Unit Quantity: 2 Pcs. Series: MM EX. Base Number: MM135EX. Harmonization Code: 8482.10.50.

Interchange guidance

The EX series is dimensioned to Ex-Cell-O inch-nominal spindle seats rather than to an ISO metric envelope, so replacement runs by the Ex-Cell-O reference number carried in the designation. Search MM135EX, MM 135 EX CR DU and MM135EXCRDU20 to reach this part.