Tapered Roller Bearing Matched Assembly 2 in Bore x 4 in OD

What this part is:
A Timken 49585-90017 tapered roller bearing assembly, 2 in bore and 4 in outside diameter, built on the 49585 cone and the 49520B cup.

Decoding the designation:
Timken numbers ending in -90xxx are assembly numbers rather than component numbers: they identify a complete bearing built and set at the factory. Here 49585 is the cone, fixing the bore, the cone width and the raceway angle, and 49520 the cup, fixing the outside diameter and the matching outer raceway, with B a Timken variant marking on that cup. The bearing is also written out as 49585/49520B.

What a matched assembly buys:
In a matched assembly the pieces are selected together and the internal geometry is controlled as a set, so the bearing arrives with its setting established rather than needing to be shimmed in on the bench. That takes out the largest single variable in tapered roller bearing life: a setting made by feel, where too much end play loads too few rollers and too much preload runs the bearing hot.

What these specs mean in practice:
Tapered roller geometry carries high radial load with substantial thrust in one direction through the raceway angle. A 2 in bore in a 4 in outside diameter is standard general-industrial and truck-driveline proportion, which is why the 49500 block is one of the most widely stocked imperial taper families.

Fitting notes:
Cup and cone are pressed home separately, each with force on its own back face and never through the rollers. The pieces of a matched assembly stay together as supplied, since the setting belongs to that combination.

Interchange guidance:
The assembly interchanges as a unit by the 49585-90017 number. The components interchange individually: a cone marked 49585 and a cup marked 49520 from another tapered roller bearing maker are the same specification, though bought loose they arrive unset. The 49576 and 49590 are different cones in the same family and are related sizes rather than substitutions.