Timken388A-3Imperial Tapered Roller Bearing Cone, 2.2650 in / 57.531 mm Bore, Class 3 Precision, Mates Cup 382A – 1 Pc

Product Description

What this part is

This is an imperial single-row tapered roller bearing cone — the inner ring together with its tapered rollers and cage. It is one half of a tapered roller bearing. The mating cup (outer race) is a separate part number and is not included in this listing.

Decoding the designation

388A is the Timken imperial cone number; its matching cup is 382A, so a complete single-row bearing is a 388A cone plus a 382A cup. The trailing -3 (also written *3 or #3) is Timken’s precision Class 3 designation. Timken’s tapered roller classes run Class 4 (standard commercial), then Class 3, Class 0 and Class 00 in increasing precision, so a Class 3 cone is held to tighter bore and running-accuracy tolerances than the standard part.

Published dimensions

Cone bore (d): 2.2650 in / 57.531 mm
Inner ring width (B): 0.8640 in / 21.946 mm
Mating cup 382A outside diameter (D): 3.8125 in / 96.838 mm
Mating cup 382A width (C): 0.6250 in / 15.875 mm
Cone weight: 5.51 lb / 2.499 kg

Published ratings and mounting data

The ratings below are catalogue values for the complete 388A/382A single-row assembly, not for the cone by itself.

Dynamic radial rating C1 (1 million rev basis): 24,200 lbf / 108,000 N
Dynamic radial rating C90 (90 million rev basis): 6,280 lbf / 28,000 N
Dynamic axial rating Ca90: 3,810 lbf / 16,900 N
Static radial rating C0: 24,100 lbf / 107,000 N
K factor: 1.65 · e: 0.35 · Y: 1.69 · geometry factor Cg: 0.0859
Effective load centre: −0.12 in / −3.0 mm (inside the cone backface)
Maximum shaft fillet radius cleared: 0.14 in / 3.600 mm
Shaft backing shoulder diameter, frontface (da): 2.48 in / 63 mm
Shaft backing shoulder diameter, backface (db): 2.76 in / 70 mm

What these specs mean in practice

Class 3 precision is worth paying for in two situations: where the cone must run true enough to hold a gear or pinion in mesh without wander, and where a matched pair is being set to a preload rather than an end play, because tighter width and bore tolerances make the set predictable instead of a trial-and-error shim exercise. The K factor of 1.65 tells you how much thrust this geometry generates from a given radial load — important because it is the induced thrust, not the applied load, that usually decides the life of the opposing bearing in a two-bearing shaft.

Quantity and configuration

This listing ships 1 Pc — one 388A-3 cone. No cup, no spacer, no seal. For a normal two-bearing shaft you will need two cones and two cups.

Fitting notes

Press the cone on square, driving on the backface only and never through the rollers or cage. Keep the shaft shoulder within the da/db figures above so the ring is supported and the cage is clear. Because a tapered roller bearing has no internal clearance until it is mounted, the setting — end play or preload — is established after both cups are seated, and a Class 3 cone is only worth its cost if that setting is done properly.

Interchange guidance

388A is a standardised imperial cone, so 388A cones from Timken, Bower/BCA, Koyo, NTN and Federal-Mogul interchange, and any of those makers’ 382A cups will run with it. Bear in mind that the standard-precision 388A and this Class 3 388A-3 share the same envelope but not the same tolerance grade. 382 and 382A are related cup sizes and are not identical — check the cup width against your housing before ordering, and note that 388 without the A is a separate catalogue item rather than a spelling variant.