Timken399A/394DC/X1SDouble Taper Roller Bearing Assembly TDO 2-11/16″ ID 4.331″ OD, Two Cones with Double Cup and Cone Spacer, Class 3, 4 Pcs

Product Description

What this part is

A Timken double-row tapered roller bearing assembly built from two 399A cones, one 394DC double cup and one X1S cone spacer. Bore is 2.6875 in (68.263 mm) and the cup outside diameter is 4.3307 in (110.000 mm). The arrangement is TDO — two rows sharing a single double outer race. The assembly is produced to Timken Class 3 precision.

Decoding the designation

Timken writes a multi-row inch assembly as its component numbers in sequence. 399A is the cone, 394DC the cup and X1S the cone spacer. The D suffix on a cup marks a one-piece double cup carrying two raceways and accepting two cones back to back, and the added C identifies the specific double-cup variant within that family. An X1S number is a cone spacer, distinct from a Y1S which is a cup spacer, so the spacer in this bill of material sits between the two cone backfaces. Class 3 is Timken’s precision grade, written elsewhere as -3, *3 or #3.

What these specs mean in practice

A TDO assembly carries radial load and thrust in both directions from a single bearing position, and the two rows share the radial load, so the same envelope carries substantially more than a single-row tapered bearing on the same bore. The cone spacer fixes the row spacing and therefore the internal setting, so the bench endplay is established at manufacture and travels with the assembly rather than being adjusted during installation. Class 3 tightens bore, outside diameter and running accuracy above standard tolerance, which matters where the bearing sets a shaft or spindle position.

Quantity and configuration

4 Pcs supplied as one matched assembly: two 399A cones, one 394DC double cup and one X1S cone spacer.

Fitting notes

The double cup is fitted in the housing bore and the two cones are clamped on the shaft against the X1S spacer, which is the standard TDO mounting with the outer race as the located member. Mounting force is applied to the ring being fitted and never transmitted through the rollers. The four components are matched, so they stay together as a set through handling and installation.

Interchange guidance

The components cross to the Timken 399A cone, Timken 394DC double cup and Timken X1S cone spacer. A 394 or 394A single cup is a related part, not an interchange, because it accepts one row only. A 399AS cone and a 394CS cup are related sizes in the same family with different back-face and raceway details. Assemblies of the same components with a different spacer width carry a different internal setting.