Timken28580-3Tapered Roller Bearing Cone Only, 2.0000 in / 50.8 mm Bore, Class 3 Precision, Mates 28521 Cup (Not Included), 1 Pc

Product Description

What this part is

A Timken 28580 tapered roller bearing cone — the inner ring complete with its roller set and cage — from the 28580/28521 single–row tapered roller bearing, supplied in Timken Class 3 precision. Bore 2.0000 in (50.8 mm), inner ring width 1.0000 in (25.4 mm). Sold as 1 Pc.

Quantity and configuration

One cone per order — 1 Pc. This is the cone only. No cup is included. A tapered roller bearing is a two–piece bearing: the cone carries the rollers, and the cup is the separate outer race they run on. The cup for this cone is the 28521 — 3.625 in (92.075 mm) outside diameter, 0.7813 in wide — giving an assembled bearing of 2 x 3.625 x 0.9688 in overall. Without a cup, the cone cannot run.

Decoding the designation

28580 — the industry–standard cone number for this size. The digits are common across brands.
−3, marked on the ring as *3 — the Timken tolerance class. Timken taper cones run in classes 4 (standard), 2, 3, 0 and 00 in ascending order of precision, so a Class 3 cone is held to tighter bore, width and runout tolerance than a standard part. Mounting dimensions are unchanged, so it drops straight into a standard position.
28521 — the mating cup number. Cone and cup numbers pair by roller and raceway geometry, which is why they are always quoted together. You will see this bearing written 28580/28521 or 28580–21.

What these specs mean in practice

Tapered roller bearings carry heavy radial load and heavy one–direction thrust at once, because the rollers and both raceways converge on a common apex. They are therefore mounted in opposed pairs: each bearing takes thrust one way, and the pair together locates the shaft and lets you set endplay or preload with the adjusting nut.

One number on this bearing looks wrong and is not. The cone is 1.0000 in wide, yet the assembled bearing measures only 0.9688 in overall. That is normal tapered–roller geometry: the small end of the cone projects past the face of the cup, so the cone alone is wider than the cone–plus–cup stack. Use 0.9688 in when you are working out the bearing seat width and 1.0000 in when you are checking cone clearance against a shoulder or seal.

Class 3 precision is worth having where shaft position matters — gear meshes, pinion settings, spindles. Tighter bore and runout tolerance means less of the setting is guesswork and the roller path stays truer under load.

Published ratings and mounting data

Cone bore 2.0000 in / 50.8 mm.
Cone (inner ring) width through bore B 1.0000 in / 25.4 mm.
Mating cup 28521: outside diameter 3.625 in / 92.075 mm, cup width 0.7813 in.
Assembled 28580/28521 bearing: 2 x 3.625 x 0.9688 in / 50.8 x 92.075 x 24.608 mm.
Timken tolerance Class 3.
Load ratings are published for the complete cone–plus–cup assembly; a cone on its own carries no independent rating.

Fitting notes

Press the cone onto the shaft against its backface, never through the rollers. Press the cup squarely and fully to its housing shoulder — a cocked cup is the commonest cause of a rebuilt taper bearing running hot, and it will not correct itself under load.

Then set the pair. Rotate the shaft under light load to seat the rollers before taking the final endplay or preload reading, because rollers that have not seated read as clearance you do not actually have. Work to the machine builder’s setting spec rather than by feel; taper bearings are far less forgiving of a guessed setting than a ball bearing is.

Interchange guidance

28580 is an industry–standard cone number, so Timken 28580, Bower/BCA 28580, Koyo 28580 and NTN 4T–28580 are the same cone on the same envelope, and all mate with a 28521 cup. The plain 28580 without a class suffix is the standard–precision build — dimensionally interchangeable, so a related build on the same envelope rather than a different part. There is also a 28580/28521–B variant with a slightly different assembled width; treat that as a related build and check the width before ordering it as a substitute. Do not pair this cone with a cup from another number family: the pairing sets the contact geometry, and matching diameters alone is not enough.